[IMP] git-mig-auto-msg: use / instead of @ in upgrade commit mess…

…ages

I don't know I had in mind 6 years ago, but `/` is a better choice:

 - It match the directory structure
 - It's easier to type on keyboard (but you don't have to if you use this
   script)
 - It's less visually disturbing

git-mig-auto-msg

@@ -85,7 +85,7 @@ def main(tag=None, message=None, coauthors=(), amend=False):
         agg_mod = {k for k, v in mods.items() if v == common_versions}
         if not agg_mod:
             break
-        agg.append('{}@{}'.format(rs(agg_mod), rs(common_versions)))
+        agg.append('{}/{}'.format(rs(agg_mod), rs(common_versions)))
         new_mods = defaultdict(set)
         for m in mods:
             v = mods[m] - common_versions
@@ -94,7 +94,7 @@ def main(tag=None, message=None, coauthors=(), amend=False):
         mods = new_mods
 
     for m, v in mods.items():
-        agg.append('{}@{}'.format(m, rs(v)))
+        agg.append('{}/{}'.format(m, rs(v)))
 
     if tag is None:
         tag = guess_tag