urlutil: provide some information about "bad url" when processing `pushurl`

It appears pushurl only support `<proto>://` entries. This is not obvious and
can lead to obscure error. We make the error less obscure as a start..

Differential Revision: https://phab.mercurial-scm.org/D10455

mercurial/utils/urlutil.py

@@ -742,7 +742,9 b' def pushurlpathoption(ui, path, value):'
     u = url(value)
     # Actually require a URL.
     if not u.scheme:
-        ui.warn(_(b'(paths.%s:pushurl not a URL; ignoring)\n') % path.name)
+        msg = _(b'(paths.%s:pushurl not a URL; ignoring: "%s")\n')
+        msg %= (path.name, value)
+        ui.warn(msg)
         return None
 
     # Don't support the #foo syntax in the push URL to declare branch to

tests/test-paths.t

@@ -175,7 +175,7 b" unknown sub-options aren't displayed"
   > EOF
 
   $ hg paths
-  (paths.default:pushurl not a URL; ignoring)
+  (paths.default:pushurl not a URL; ignoring: "/not/a/url")
   default = /path/to/nothing
 
 #fragment is not allowed in :pushurl