don't call xcache_clear_cache on clearOpcodeCache() in case admin auth is enabled for xcache in php.ini
don't use xcache in case admin auth is enabled in php.ini - this can cause issues
Do not define xcache_unset_by_prefix() if it does not exist.

The defined function is not compatible with the function provided by xcache
because it does not honor the prefix parameter. Thus defining it like this is
a bad idea.
Allow usage of xCache variable cache if xcache_unset_by_prefix() is present.
Clear xCache OpCode cache instead of variable cache in clearOpcodeCache().
xcache_unset_by_prefix() returns feedback, return it.
Add link to XCache API in class documentation.
xCache -> XCache
Make it clear that log message is about the XCache opcode cache.
Do not mention php.ini, it may be defined in xcache.ini or so.
Move core setup code to controller class
Check for failure in creating htaccessWorking testfile
Merge branch 'master' into setup

Conflicts:
	lib/util.php
fixing typo on $htaccessWorking - testing own code before pushing is appreciated
Added support for extra backends

Somebody had forgotten "OC_User::setupBackends();"...
Copyright and small fix
Merge remote-tracking branch 'origin/master' into setup
Converts em to px values for styles in Files.
Cleans up Core apps for relative(em) to absolute(px) styles.
All Core Styles from em->px, apart from styles.css