\Log::_init() - Extended determinig name and logation of logfile by new config "log_filename"

log_filename = 'fuelphp.log' - for loging is used only this one file in log_path dir.
log_filename = null - use original way

I made this extension, because I want use linux logrotation

Signed-off-by: Kristián Feldsam <feldsam@gmail.com>
Added "log_filename" entry to config. REFS #1648

Signed-off-by: Kristián Feldsam <feldsam@gmail.com>
fix #1649

Fix for removal of staticExpects in PHPUnit 4 by introducing 
Test_Router_Mock.
Merge pull request #1648 from MyMedia/1.8/develop

\Log::_init() - Extended determinig name and location of logfile by new ...
some log cleanup. related #1648
Merge pull request #1651 from CodeYellowBV/1.8/develop

fix #1649
make sure html_tag() generates compliant HTML. closes #1616

modified due to lack of response of the original PR author.
avoid deadlocks which empty cache files, closes #1632

this should not happen, but just in case...
Improve cli backtrace. closes #1634

rewrite due to coding standard violations and lack of response from the
PR author. also added missing new config key
Recurse fieldset validation

By doing this, subclasses of Fieldset get the opportunity to
validate themselves from the input, rather than having the parent
do all the work and make possibly false assumptions.
Fix epic fail in recursive validation
Create set_input() on validation so extensions can override it
Same recursive idea in repopulate()