commands: Add 'hg log --branch' and deprecate 'hg log --only-branch'
Switching to --branch makes log consistent with push/pull and make more sense
given the actual behavior of the option (you can specify -b multiple times to
include multiple branches).
This change also adds some tests for 'hg log -b'.
adding a/b/c/d/x
adding a/b/c/d/y
adding a/b/c/d/z
moving a/b/c/d/x to z/b/c/d/x
moving a/b/c/d/y to z/b/c/d/y
moving a/b/c/d/z to z/b/c/d/z