templatekw: use ctx.rev() instead of casting context to int
basectx has __int__ implemented. Per mailing list discussion
with Yuya, we don't like having this implemented because it is
too much magic and in some cases rev() will return None, which
isn't an int.
So convert a `'%d' % ctx` to ctx.rev() instead.
Differential Revision: https://phab.mercurial-scm.org/D2423
Greg Ward, author of the original bfiles extension
Na'Tosha Bard of Unity Technologies
Fog Creek Software
Special thanks to the University of Toronto and the UCOSP program