Cache Optimization + bug fixes

[ghost]

In brief:

• before: 80,098 allocs, 80,073 frees, 50,238,672 bytes allocated
• after: 79,686 allocs, 79,661 frees, 15,219,256 bytes allocated

Tested with

USE_ZEND_ALLOC=0 valgrind $(phpenv which php) unit-tests/manual-unit.php CacheTest.php CacheTest

Bug fixes:

• 6c37bad: looks like it is not always safe to store zval** as references to properties in PHP 5.4+ (zval** points to the location where the property is stored and the properties sometimes migrate); this will probably fix the bug with crashing session bag
• c46c766 implements Phalcon\Cache\Backend\Memory::queryKeys()
• 00f2177 adds checks to phalcon_call_XXX to ensure that all arguments are zval*'s
• e69c7ba fixes bugs in Libmemcached that crippled past the review

[phalcon]

Great!