convert/svn: fix _iterfiles() output in root dir case (issue2647)

When converting directory additions/replacement with project directory set to
root, _iterfiles() sometimes returned paths starting with a slash making
following svn calls to fail.

I could not reproduce the issue with hand-crafted repositories.

Report and first analysis by Clinton Chau <[e-mail]>

hgext/convert/subversion.py

@@ -866,7 +866,9 b' class svn_source(converter_source):'
         pool = Pool()
         rpath = '/'.join([self.baseurl, urllib.quote(path)]).strip('/')
         entries = svn.client.ls(rpath, optrev(revnum), True, self.ctx, pool)
-        return ((path + '/' + p) for p, e in entries.iteritems()
+        if path:
+            path += '/'
+        return ((path + p) for p, e in entries.iteritems()
                 if e.kind == svn.core.svn_node_file)
 
     def getrelpath(self, path, module=None):