hgweb: use heads() instead of headrevs()

These appear to be the only callers of headrevs() on file storage
objects. Let's port to heads() so we can remove headrevs().

Differential Revision: https://phab.mercurial-scm.org/D4662

mercurial/hgweb/webcommands.py

@@ -143,7 +143,7 b' def _filerevision(web, fctx):'
     f = fctx.path()
     text = fctx.data()
     parity = paritygen(web.stripecount)
-    ishead = fctx.filerev() in fctx.filelog().headrevs()
+    ishead = fctx.filenode() in fctx.filelog().heads()
 
     if stringutil.binary(text):
         mt = mimetypes.guess_type(f)[0] or 'application/octet-stream'
@@ -922,7 +922,7 b' def annotate(web):'
     fctx = webutil.filectx(web.repo, web.req)
     f = fctx.path()
     parity = paritygen(web.stripecount)
-    ishead = fctx.filerev() in fctx.filelog().headrevs()
+    ishead = fctx.filenode() in fctx.filelog().heads()
 
     # parents() is called once per line and several lines likely belong to
     # same revision. So it is worth caching.