Fix wfCheckLimits was deprecated in MediaWiki 1.24
Merge pull request #355 from SemanticMediaWiki/mw-124

Fix wfCheckLimits was deprecated in MediaWiki 1.24
Add HttpRequest / CurlRequest / HttpResponseFilter

- Move SparqlDatabaseException into its own file
- Start to use HttpRequest / CurlRequest instead of relying on curl_* calls
- Move Error handling to HttpResponseFilter
- Some tidy