merge default into stable for 2.8 freeze

discovery: revise hint message introduced by changeset b00ba31313c3 This patch revises hint message from "for detail about" introduced by changeset b00ba31313c3 to "for details about", to unify it with the hint message introduced by proceeding patch.

push: add more detailed explanation about "--force" to online help document This patch adds more detailed explanation about "--force" to online help document of "hg push" to prevent novice users to execute "push --force" easily without understanding about problems of multiple branch heads in the repository.

push: hide description about "-f" in the hint to prevent from using it easily "use push -f to force" in the hint at abortion of "hg push" may cause novice users to execute "push -f" easily without understanding about problems of multiple branch heads in the repository. This patch hides description about "-f" in the hint, and leads into seeing "hg help push" for details about pushing new heads.

demandimport: allow extensions to import own modules by absolute name Before this patch, python modules of each extensions can't import another one in own extension by absolute name, because root modules of each extensions are loaded with "hgext_" prefix. For example, "import extroot.bar" in "extroot/foo.py" of "extroot" extension fails, even though "import bar" in it succeeds. Installing extensions into site-packages of python library path can avoid this problem, but this solution is not reasonable in some cases: using binary package of Mercurial on Windows, for example. This patch retries to import with "hgext_" prefix after ImportError, if the module in the extension may try to import another one in own extension. This patch doesn't change some "_import()"/"_origimport()" invocations below, because ordinary extensions shouldn't cause such invocations. - invocation of "_import()" when root module imports sub-module by absolute path without "fromlist" for example, "import a.b" in "a.__init__.py". extensions are loaded with "hgext_" prefix, and this causes execution of another (= fixed by this patch) code path. - invocation of "_origimport()" when "level != -1" with "fromlist" for example, importing after "from __future__ import absolute_import" (level == 0), or "from . import b" or "from .a import b" (0 < level), for portability between python versions and environments, extensions shouldn't cause "level != -1".

demandimport: support "absolute_import" for external libraries (issue4029) Before this patch, demandimport of Mercurial may fail to load external libraries using "from __future__ import absolute_import": for example, importing "foo" in "bar.baz" module will load "bar.foo" if it exists, even though "absolute_import" is enabled in "bar.baz" module. So, extensions for Mercurial can't use such external libraries. This patch saves "level" of import request for on-demand module loading in the future: default value of level is -1, and level is 0 when "absolute_import" is enabled. "level" value is passed to built-in import function in "_demandmod._load()" and it should load target module correctly. This patch changes only one "_demandmod" construction case other than cases below: - construction in "_demandmod._load()" this code path should be used only in relative sub-module loading case - constructions other than patched one in"_demandimport()" these code paths shouldn't be used in "level != -1" case

hghave: add "py3k" feature to check whether test runs with Python 3.x This patch adds "py3k" feature to check whether test runs with Python 3.x. This check is needed for portability of test code: for example, in the default, modules are imported relatively first with python 2.x, but imported absolutely with Python 3.x.

hghave: add "absimport" feature to check "absolute_import" in __future__ This patch adds "absimport" feature to check whether "absolute_import" exists in __future__, which means supporting module loading by absolute name. This check is needed for portability of test code using "absolute_import", because Python earlier than 2.5 doesn't support it.

merge: exit early during a no-op update (BC) hg update . (or equivalents) are effectively no-ops in just about all circumstances. These sorts of updates can be especially common in a bookmark-oriented workflow. This saves us a status check and a manifest decompression, which means that on a repo with over 210,000 files, this brings hg update . down from 2.5 seconds to 0.15. There is one change in behavior: a file that was added, not committed, and then deleted but not removed used to be removed from the dirstate. With this patch it isn't. This is what causes the change in test-mq-qpush-exact.t. This seems like it's enough of an edge case to not be worth handling. The output of test-empty.t changes because those files are not yet created.

localrepo: invoke only feature setup functions for enabled extensions Before this patch, each feature setup functions for localrepository class should examine whether corresponding extension is enabled or not by themselves. This patch invokes only feature setup functions defined in module of enabled extensions, and it makes implementation of feature setup functions easier and simpler.