add mapnik_version_from_string helper function

CHANGELOG

@@ -14,6 +14,9 @@ For a complete change history, see the SVN log.
 Mapnik Trunk
 ------------
 
+- Added 'mapnik_version_from_string()' function in python bindings to easily convert string representation
+  of version number to the integer format used in 'mapnik/version.hpp'. e.g. '0.7.1' --> 701.
+
 - Added xinclude (http://www.w3.org/TR/xinclude/) support to libxml2-based xml parser (oldtopos) (#567)
 
 - Optimized rendering speeds by avoiding locking in the projection code (r2063)

bindings/python/mapnik/__init__.py

@@ -601,14 +601,18 @@ def Kismet(**keywords):
     keywords['type'] = 'kismet'
     return CreateDatasource(keywords)
 
-def mapnik_version_string():
+def mapnik_version_string(version=mapnik_version()):
     """Return the Mapnik version as a string."""
-    version = mapnik_version()
     patch_level = version % 100
     minor_version = version / 100 % 1000
     major_version = version / 100000
     return '%s.%s.%s' % ( major_version, minor_version,patch_level)
 
+def mapnik_version_from_string(version_string):
+    """Return the Mapnik version from a string."""
+    n = version_string.split('.')
+    return (int(n[0]) * 100000) + (int(n[1]) * 100) + (int(n[2]));
+
 def register_plugins(path=inputpluginspath):
     """Register plugins located by specified path"""
     DatasourceCache.instance().register_datasources(path)