templatefilters: rename commonprefix to commondir...
templatefilters: rename commonprefix to commondir
Two reasons:
* It makes it clearer that it's not a generic common string
prefix (e.g. commonprefix(["bar", "baz"]) is not "ba", but "")
* If we ever want a filter for generic common string prefix,
then the name is now available for that.
"commondir" does not describe the prefix-ness, however. I'm happy to
rename it "commondirprefix" or "commonprefixdir" if others prefer.
Differential Revision:
https://phab.mercurial-scm.org/D3731
