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.

mercurial/templatekw.py

@@ -325,11 +325,15 b' def showfiles(**args):'
     """
     return showlist('file', args['ctx'].files(), **args)
 
-def showlatesttag(repo, ctx, templ, cache, **args):
-    """:latesttag: String. Most recent global tag in the ancestors of this
-    changeset.
+def showlatesttag(**args):
+    """:latesttag: List of strings. The global tags on the most recent globally
+    tagged ancestor of this changeset.
     """
-    return ':'.join(getlatesttags(repo, ctx, cache)[2])
+    repo, ctx = args['repo'], args['ctx']
+    cache = args['cache']
+    latesttags = getlatesttags(repo, ctx, cache)[2]
+
+    return showlist('latesttag', latesttags, separator=':', **args)
 
 def showlatesttagdistance(repo, ctx, templ, cache, **args):
     """:latesttagdistance: Integer. Longest path to the latest tag."""

tests/test-tag.t

@@ -458,6 +458,9 b' check that we can merge tags that differ'
   $ echo c4 > f4
   $ hg log -r '.' -T "{changessincelatesttag} changes since {latesttag}\n"
   2 changes since t4:t6
+  $ hg log -r '.' -T "{latesttag % '{latesttag}\n'}"
+  t4
+  t6
   $ hg ci -A -m4
   adding f4
   $ hg log -r 'wdir()' -T "{changessincelatesttag} changes since {latesttag}\n"