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.
Merge remote-tracking branch 'owncloud/master' into fixing-3417-master

* owncloud/master: (1989 commits)
  [tx-robot] updated from transifex
  dont try to register background jobs if we haven't upgraded yet
  adjust test
  coding style
  coding style
  On webdav sesssions, loginname was compared to username which does not need to match necessarily
  rely only on php DateTime to parse the db datetime string
  LDAP: fix method behind save button on advancend and expert tabs, fixes at least Home Folder setinng
  Fix webroot for update page
  Update 3rdparty ref
  update 3rdparty
  toggle select all checkbox
  remove unneeded ; in comment
  LDAP: the browser shall not autofill userdn and password, usually login credentials are inserted. fixes #6283
  Add test for having utf8 filenames in the cache
  fix fallback overwriting result of getHome
  [tx-robot] updated from transifex
  fix smbclient directory listing parser
  cache the home folder of a User
  Send "SET NAMES utf8" to MySQL for PHP below 5.3.6
  ...

Conflicts:
	lib/util.php
Merge remote-tracking branch 'owncloud/master' into fixing-3417-master

* owncloud/master: (30 commits)
  Added entry with ext storage info
  [tx-robot] updated from transifex
  [tx-robot] updated from transifex
  clarifying license
  remove unused method tail()
  reliable detect encrypted files
  [tx-robot] updated from transifex
  remove duplicated code
  add missing quotes + field declarations
  Do not use xcache variable cache if cache size is 0.
  always show home breadcrumb in files view
  Use DEBUG instead of ERROR when favourites not found. Fix #6419
  update file cache for target file
  only remove encryption keys if a real file gets deleted, skip this method if a file outside of /data/user/files was deleted
  Fixed JS plural function to be per app
  call set password hook because it doesn't get triggered during test execution and fix paths
  Do not use L10n when logging exceptions
  Also add default to the \OCP\IConfig interface
  add default parameter for AllConfig->get*Value()
  always show 'Deleted Files' breadcrumb
  ...

Conflicts:
	lib/private/memcache/xcache.php
Merge pull request #4378 from owncloud/fixing-3417-master

Don't use xcache in case admin auth is enabled