Only compile the version string regex once on module import.

* MOVE the compiled regex for matching the GnuPG binary's version to a
   module-level variable in `gnupg._util`.

gnupg/_util.py

@@ -70,6 +70,9 @@ _conf = os.path.join(os.path.join(_user, '.config'), 'python-gnupg')
 ## Logger is disabled by default
 log = _logger.create_logger(0)
 
+#: Compiled regex for determining a GnuPG binary's version:
+_VERSION_STRING_REGEX = re.compile('(\d)*(\.)*(\d)*(\.)*(\d)*')
+
 
 def find_encodings(enc=None, system=False):
     """Find functions for encoding translations for a specific codec.
@@ -436,8 +439,7 @@ def _match_version_string(version):
 
     :param str version: A version string in the form x.x.x
     """
-    regex = re.compile('(\d)*(\.)*(\d)*(\.)*(\d)*')
-    matched = regex.match(version)
+    matched = _VERSION_STRING_REGEX.match(version)
     g = matched.groups()
     major, minor, micro = int(g[0]), int(g[2]), int(g[4])
     return (major, minor, micro)