convert: tolerate trailing spaces on map files

A convert run with a branchmap made with

echo default namedbranch > branchmap

on Windows fails silently and surprisingly; it actually
adds a space after 'namedbranch', so it ends up mapping
"default namedbranch" to "".

This also affects splicemaps, since the same parser is used
for both.

hgext/convert/common.py

@@ -384,7 +384,7 b' class mapfile(dict):'
             return
         for i, line in enumerate(fp):
             try:
-                key, value = line.splitlines()[0].rsplit(' ', 1)
+                key, value = line.splitlines()[0].rstrip().rsplit(' ', 1)
             except ValueError:
                 raise util.Abort(
                     _('syntax error in %s(%d): key/value pair expected')