Merge pull request #2699 from vlakoff/url-functions

Implement $protocol parameter in Config base_url() and site_url() methods
Fix CI_DB_query_builder::_merge_cache() triggering E_WARNINGs

Kudos to kakysha for noting the bug & providing initial fix in PR #2698
Fixing the dumbest parser error ever
Fix #2703
Really fix #2703
Merge branch 'develop' of github.com:EllisLab/CodeIgniter into develop