try if grass module can be imported

git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@10817 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: rblazek

src/plugins/grass/scripts/qgis.db.connect-login.pg.py

@@ -72,7 +72,10 @@
 import sys
 import os
 import string
-import grass
+try:
+    import grass
+except:
+    raise Exception ("Cannot find 'grass' Python module. Python is supported by GRASS from version 6.4" )
 
 def main():
     host = options['host']