narrowwirepeer: rename expandnarrow capability to exp-expandnarrow

The expandnarrow functionality lets a client have a shorthand (for
Google it's a reference to a checked-in file) for a set of includes
and excludes. For testing we should probably implement a simple
version of that functionality here. For now, rename the capability so
we don't burn the good name in the future if we need to change
behavior.

It's plausible that this functionality should be dropped from the
narrowhg we ship long-term, but I'm dubious as it seems pretty likely
other organizations will want similar shorthands for commonly-used
subsets of their trees.

Differential Revision: https://phab.mercurial-scm.org/D2193

hgext/narrow/narrowwirepeer.py

@@ -24,7 +24,7 def uisetup():
         class expandingpeer(peer.__class__):
             def expandnarrow(self, narrow_include, narrow_exclude, nodes):
                 ui.status(_("expanding narrowspec\n"))
-                if not self.capable('expandnarrow'):
+                if not self.capable('exp-expandnarrow'):
                     raise error.Abort(
                         'peer does not support expanding narrowspecs')