Merged pull request #385
PHP-737: Remove invalid argument casting

Possibly a copy-paste error. This cast was necessary in php_mongo_ctor() since error_message was a (char *), but it's alreay of the appropriate type here.
Be more conservative with malloc() for RP tags error message

This is consistent with error message allocation in mongo_store_option().
Merged Pull Request #387

# By Jeremy Mikola
* pull-request/387:
  Be more conservative with malloc() for RP tags error message
  PHP-737: Remove invalid argument casting
Enable PHP5.2 builds on Travis

Note: 5.2 doesn't have -g, so set it in the environment so the others
can pick it up.
Also, 5.2 is very picky on the extension_dir it seems, so we need to set
it, because it doesn't support relative paths from `php`