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

mercurial/templatekw.py

@@ -400,7 +400,7 b' def showchildren(**args):'
     """List of strings. The children of the changeset."""
     args = pycompat.byteskwargs(args)
     ctx = args['ctx']
-    childrevs = ['%d:%s' % (cctx, cctx) for cctx in ctx.children()]
+    childrevs = ['%d:%s' % (cctx.rev(), cctx) for cctx in ctx.children()]
     return showlist('children', childrevs, args, element='child')
 
 # Deprecated, but kept alive for help generation a purpose.