share: use defaultdest to compute unspecified destination stable

share: use defaultdest to compute unspecified destination

This harmonizes with clone, and avoids creating a .hg in the current directory if
the source ends with a /

--- a/mercurial/hg.py	Fri Dec 18 15:05:42 2009 -0500
+++ b/mercurial/hg.py	Sat Dec 19 22:55:33 2009 -0800
@@ -88,7 +88,7 @@
         raise util.Abort(_('can only share local repositories'))
 
     if not dest:
-        dest = os.path.basename(source)
+        dest = defaultdest(source)
     else:
         dest = ui.expandpath(dest)