#015227: Race condition in ezcCacheStorageFile::lock() causes E_WARNING

When the lock file gets deleted while ezcCacheStorageFile::lock() waits for the lock, a E_WARNING error gets throwed because it tries to use filemtime() on the lock file (that doesn't exist anymore) to check if the lock is dead.

Warning: filemtime(): stat failed for /tmp/cache/test/.ezcLock in /usr/share/php/ezc/Cache/storage/file.php on line 735

Call Stack:
    0.0004     100696   1. {main}() /home/jou/dev/ezc_cache_race_condition.php:0
    0.0126     802080   2. ezcCacheStorageFile->lock() /home/jou/dev/ezc_cache_race_condition.php:13
    1.0129     802264   3. filemtime() /usr/share/php/ezc/Cache/storage/file.php:735

Warning: unlink(/tmp/cache/test/.ezcLock): No such file or directory in /usr/share/php/ezc/Cache/storage/file.php on line 737

Call Stack:
    0.0004     100696   1. {main}() /home/jou/dev/ezc_cache_race_condition.php:0
    0.0126     802080   2. ezcCacheStorageFile->lock() /home/jou/dev/ezc_cache_race_condition.php:13
    1.0131     802320   3. unlink() /usr/share/php/ezc/Cache/storage/file.php:737

We either need a file_exists() check before calling filemtime() or a shut-up operator infront of the filemtime() and unlink() calls.

Operating System:
PHP Version: (please be specific, like '4.4.3' or '5.1.5')
Database and version:
Browser (and version):

Execute attached test case in two shells in parallel. The process that get started later throws the error.