Implement $protocol parameter in Config base_url() and site_url() methods

Let's keep the implementation logic in one place.
Improves 2023c3d05b042cf1322286d69557c2b8bf3bd8d5.
Remove redundant changelog entry
Fix CI_DB_query_builder::_merge_cache() triggering E_WARNINGs

Kudos to kakysha for noting the bug & providing initial fix in PR #2698
An alternative to CI_Output::_minify_script_style() using more efficient regexp patterns
Fixing the dumbest parser error ever
Fix #2703
Really fix #2703
Added option to connect through unix socket in redis cache driver
Correct Redis connection troubleshooting
some code rewrite
Code cleanup
Update Redis Caching block

Added config options
Added changelog entry
Spaces, log message
typos
Update caching.rst
newline at the eof
Update readme.rst
add travis php 5.5
Update sess_time_to_update description (rel #2397)