Improve output cache.
Merge branch 'develop' of https://github.com/EllisLab/CodeIgniter into feature/output-cache-improvements
Replace is_null() with === / !== NULL

Exact same behavior, but faster. I also think it's more readable.
[ci skip] Fix issue #2157 - docs on the email library
A few adjustments to previous commit
Merge pull request #2152 from vlakoff/develop

Replace is_null() with === / !== NULL
Merge branch 'develop' of https://github.com/EllisLab/CodeIgniter into feature/output-cache-improvements
Fix issues #2160, #2161
Fix and optimize auto_link() URL helper function.

Signed-off-by: Eric Roberts <eric@cryode.com>
Return spacing on var definitions.

Signed-off-by: Eric Roberts <eric@cryode.com>
Merge pull request #2151 from cryode/feature/output-cache-improvements

Add headers to Output class cache files.
Remove whitespace from empty lines.

Signed-off-by: Eric Roberts <eric@cryode.com>
Support minify table block
Merge pull request #2171 from purwandi/minify-table-block

Support minify table block in output
[ci skip] Add text/plain as a valid MIME for js,css,*html,xml
[ci skip] Manually apply #2162, #2163
Partially implement PR #2155
Adjust regex.
Merge pull request #2164 from cryode/bug/auto_link

Fix and optimize auto_link() URL helper function.
Update application/config/config.php