templatekw: make {latesttag} a hybrid list
This maintains the previous behavior of expanding {latesttag} to a string
containing all of the tags, joined by ':'. But now it also allows list type
operations.
I'm unsure if the plural handling is correct (i.e. it seems like it is usually
"{foos % '{foo}'}"), but I guess we are stuck with this because the singular
form previously existed.
To run the tests, do:
cd tests/
python run-tests.py
See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.