import: add help examples

id: add some help examples

export: add help examples

diff: add help examples

archive: add help examples

test-rollback: tinker a bit to make it easier to add more tests.

convert: added bookmarks support in filemap When using the convert extension from a Mercurial rep. to subset it with filemap, the bookmarks are not copied. I fixed this by calling the base.get_bookmarks() from the filemap getbookmarks() instead of returning an empty dictionary. It should work also for other converters that implement getbookmarks() (like git). I don't see any drawbacks except that the bookmarks are always copied (not necessarily wanted all the times).

util: fix finding of hgexecutable The version introduced in 89d9f92f6fdd would for example return thg (thanks to Mads Kiilerich for pointing to this)

log: add a usage note about --removed

log: rearrange the help text a bit