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.
preserve 3rd party values in  in the Session destructor
check if a $_SESSION entry exists before we try to remove it
Fixed download file from URL error messages

- L10N now converted to string to make them work with json_encode
- Added specific error message when server doesn't allow fopen on URLs
- Fixed client side to correctly show error message in a notification
- Added OCP\JSON::encode() method to encode JSON with support for the
  OC_L10N_String values
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
Do not use xcache variable cache if cache size is 0.

This is possible because it is possible to only use xcache as an opcode cache
but not a variable cache.
remove duplicated code
remove unused method tail()
DB: Support DECIMAL(precision,scale) syntax in XML

Add support for specifying the precision and scale of a decimal data
type to the XML description language.

See owncloud/core#6475
Add decimal(precision,scale) column to unit tests
Typo fixed