merge with stable

help: basic support for showing only specified topic sections For instance, 'hg help config.files' will show only the Files section.

help: use OS containers for config file lists

help: support OS-specific help sections Containers of the form: .. container:: verbose.<os> are shown by default on the given OS (or with -v).

minirst: allow multiple container types for prune If we have a container of type x.y, then we can preserve it by keeping x or y.

config: don't read the same config file twice In some cases some config files would be read twice and shown twice in showconfig --debug.

templater: fix precedence of --style and --template options Since e3eb480a9391, --template option is ignored if --style is specified, which is wrong according to the doc of show_changeset(): Display format will be the first non-empty hit of: 1. option 'template' 2. option 'style' ...

shelve: avoid writing file that is never read from The contents of the .files file has not been used since 1d7a36ff2615 (shelve: use rebase instead of merge (issue4068), 2013-10-23), so stop writing it. Where we currently use the presence of the file as a check for a valid shelve name, switch to checking for the .patch file.

hgk: don't break on repositories with obsolete changesets Check the existence of a changeset before adding it to the list returned by debug-rev-list command.

test: protect the run-tests.py --json test behind an hghave rule We add a rules to detect availability of a json module and skip if json is not available.