stack: strip trailing dots from short_name

Fixes assertion failure which can occur because the short_name is a
truncated version of the already-sanitized long_name, but the
truncation may leave a trailing dot.

stgit/lib/stack.py

@@ -213,6 +213,9 @@ def make_name(self, raw, unique=True, lower=True, allow=(), disallow=()):
                 short_name = new_name
             else:
                 break
+        # Strip trailing dots again because the truncation may have
+        # left a trailing dot, which is not allowed
+        short_name = re.sub(r'\.+$', '', short_name)
         assert self.is_name_valid(short_name)
 
         if not unique: