util: extract function that parses timezone string

It will be used to parse a timezone argument passed to a template function.

mercurial/util.py

@@ -1371,11 +1371,8 def shortdate(date=None):
     """turn (timestamp, tzoff) tuple into iso 8631 date."""
     return datestr(date, format='%Y-%m-%d')
 
-def strdate(string, format, defaults=[]):
-    """parse a localized time string and return a (unixtime, offset) tuple.
-    if the string cannot be parsed, ValueError is raised."""
-    def timezone(string):
-        tz = string.split()[-1]
+def parsetimezone(tz):
+    """parse a timezone string and return an offset integer"""
         if tz[0] in "+-" and len(tz) == 5 and tz[1:].isdigit():
             sign = (tz[0] == "+") and 1 or -1
             hours = int(tz[1:3])
@@ -1385,8 +1382,11 def strdate(string, format, defaults=[])
             return 0
         return None
 
+def strdate(string, format, defaults=[]):
+    """parse a localized time string and return a (unixtime, offset) tuple.
+    if the string cannot be parsed, ValueError is raised."""
     # NOTE: unixtime = localunixtime + offset
-    offset, date = timezone(string), string
+    offset, date = parsetimezone(string.split()[-1]), string
     if offset is not None:
         date = " ".join(string.split()[:-1])