rebase: factor out histedit help command

util: use tuple accessor to get accurate st_mtime value (issue4836) Because st.st_mtime is computed as 'sec + 1e-9 * nsec' and double is too narrow to represent nanoseconds, int(st.st_mtime) can be 'sec + 1'. Therefore, that value could be different from the one got by osutils.listdir(). This patch fixes the problem by accessing to raw st_mtime by tuple index. It catches TypeError to fall back to st.st_mtime because our osutil.stat does not support tuple index. In dirstate.normal(), 'st' is always a Python stat, but in dirstate.status(), it can be either a Python stat or an osutil.stat. Thanks to vgatien-baron@janestreet.com for finding the root cause of this subtle problem.

util: extract stub function to get mtime with second accuracy This function is trivial but will need a long comment why it can't use st.st_mtime. See the next patch for details.

scmutil: add a way for a repo's wlock to be inherited by a subprocess This is part of a series that will allow locks to be inherited by subprocesses in limited circumstances. In the future, we'll call this for custom merge drivers.

scmutil: add a way for a subprocess to be run with an inheritable lock This is part of a series that will allow locks to be inherited by subprocesses in limited circumstances. In an upcoming patch, we'll add an API for the wlock to be inherited.

localrepo: add a way to get the current wlock if it's held This will be useful to pass around a reference to the lock to some functions we're going to add to scmutil. We don't want those functions to live in localrepo to avoid bloat.

localrepo: add a way to get the current lock if it's held We'll use this in upcoming patches to return a reference to the wlock if it's held.

test-help: verify that extension keywords appear in help templates fixed by a2291c9c85a1

templatekw: add {changes}, {distance} and {tag} to the {latesttag} keyword

templater: introduce {latesttag()} function to match a pattern (issue4184) This allows the latest class of tag to be found, such as a release candidate or final build, instead of just the absolute latest. It doesn't appear that the existing keyword can be given an optional argument. There is a keyword, function and filter for 'date', so it doesn't seem harmful to introduce a new function with the same name as an existing keyword. Most functions are pretty Mercurial agnostic, but there is {revset()} as precedent. Even though templatekw.getlatesttags() returns a single tuple, one entry of which is a list, it is simplest to present this as a list of tags instead of a single item, with each tag having a distance and change count attribute. It is also closer to how {latesttag} returns a list of tags, and how this function works when not given a '%' operator.