Incompatibility with postgres

I've been fighting for days to get the mapper working with anything. Then I looked at the logs and found that there's an sql error. There's improper quoting happening when using postgres. In the function _feedapi_mapper_store_mapping(), the queries quote the %s value as "%s". That doesn't work with postgres. I changed it to \'%s\' and everything seemed worked fine.

Sorry I don't have time to make a proper patch. I havn't tested this with mysql to see if this will still work with it.