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.
running: init test1
result: None
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: None
running: commit -m commit2 -d 2000-01-02 foo
result: None
running: log -r 0
changeset: 0:0e4634943879
user: test
date: Sat Jan 01 00:00:00 2000 +0000
summary: commit1
result: None
running: log -r tip
changeset: 1:45589e459b2e
tag: tip
user: test
date: Sun Jan 02 00:00:00 2000 +0000
summary: commit2
result: None