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.
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1