apply patch from stella for faster sqlite reads - closes #797

CHANGELOG

@@ -14,6 +14,8 @@ For a complete change history, see the SVN log.
 Mapnik Trunk
 ------------
 
+- SQLite Plugin: optimize io using shared cache and no mutexes (#797)
+
 - Directly link input plugins to libmapnik to avoid having to set dlopen flags from binding languages (#790)
 
 - Throw an error during registration for fonts which Freetype2 does not report a family or style name (r2985).

plugins/input/sqlite/sqlite_types.hpp

@@ -122,7 +122,8 @@ public:
     sqlite_connection (const std::string& file)
         : db_(0)
     {
-        if (sqlite3_open (file.c_str(), &db_))
+        sqlite3_enable_shared_cache(1);
+        if (sqlite3_open_v2 (file.c_str(), &db_, SQLITE_OPEN_NOMUTEX|SQLITE_OPEN_SHAREDCACHE, 0))
         {
             std::ostringstream s;
             s << "Sqlite Plugin: ";