help: add documentation for new template functions

--HG--
branch : stable
log: remove any ancestors of nullrev (issue3772)

For the special case, ":null" we remove the implied revision 0 since that
wouldn't make any sense here. A test case is added to make sure only nullrev is
shown.

--HG--
branch : stable
graphmod: don't try to visit nullrev (issue3772)

--HG--
branch : stable
tests: add regression tests for another revrange edge case

These tests would've passed before ac0c12123743 and e441657b372b.
Inserting them to make sure that continues to be the case.

--HG--
branch : stable
doc: use "tag" revset predicate instead of "tagged" for example in help

"tag" predicate is officially described in help, but "tagged" is not,
even though the latter works as same as the former.

--HG--
branch : stable
extra : amend_source : ea8cf96b96f7e6e22d10a98b596700a836e385db
test-bookmarks-pushpull.t: don't set bookmark active unnecessarily

The test in question doesn't have anything to do with having an active
bookmark. This change makes the test change the two bookmarks it affects
without making them active. It clears the way for adding a test for
updating to an active bookmark that moved out from under us.

--HG--
branch : stable
extra : rebase_source : dafae5199a21f33cf53583f12ac8ada1d29ab409
update: update to current bookmark if it moved out from under us (issue3682)

If the current bookmark (the one listed in .hg/bookmarks.current)
doesn't point to a parent of the working directory, e.g. if it was moved
by a pull, use that as the update target instead of the tipmost
descendent.

A small predicate is (finally) added to the bookmarks module to check
whether the current bookmark is also active.

--HG--
branch : stable
extra : rebase_source : 021016ea7a0bf1e7b8170d78a5e362ba0aff1b5b
test-rebase: add another test for rebase with multiple roots

This test the case when a Merge is dropped.

--HG--
branch : stable