Allow regex special characters in tagstrings.

Fixes the following crashes:
1. tag completion with regex special chars
:search tag:[<tab>

2. Changing tag representation of an (existing) tag with regex special
chars:
[tags]
    [[my**tag]]
        normal = '','', 'white','light red', 'white','#d66'

3. Contact completion with regex special chars and no external command:
To:**foo<tab>

1 files changed, 1 insertions, 1 deletions

diff --git a/alot/addressbook/__init__.py b/alot/addressbook/__init__.py
index 17800b33..28c4ecc7 100644
--- a/alot/addressbook/__init__.py
+++ b/alot/addressbook/__init__.py
@@ -34,7 +34,7 @@ class AddressBook(object):
     def lookup(self, query=''):
         """looks up all contacts where name or address match query"""
         res = []
-        query = re.compile('.*%s.*' % query, self.reflags)
+        query = re.compile('.*%s.*' % re.escape(query), self.reflags)
         for name, email in self.get_contacts():
             if query.match(name) or query.match(email):
                 res.append((name, email))