sshrepo: add more safe characters (issue2983)

Extended the list of safe characters introduced in 86fc364ca5f8 to include
everything from pipes._safechars, which is only available on Unix platforms.
Place "-" at the end of the range to avoid backslash-escape.
New characters: @%+=:,

mercurial/sshrepo.py

@@ -21,7 +21,7 b' class remotelock(object):'
 
 def _serverquote(s):
     '''quote a string for the remote shell ... which we assume is sh'''
-    if re.match(r'[a-zA-Z0-9._\-/]*$', s):
+    if re.match('[a-zA-Z0-9@%_+=:,./-]*$', s):
         return s
     return "'%s'" % s.replace("'", "'\\''")