prepare ext_memcache and ext_memcached for references deprecation
Summary:
### ext_memcache
Remove optional &$flags parameter from Memcache::get and memcache_get. This parameter was never populated in C++ anyway.
### ext_memcached
Introduce the following inout functions:
```
Memcached::getWithCasToken()
Memcached::getByKeyWithCasToken()
Memcached::getMultiWithCasTokens()
Memcached::getMultiByKeyWithCasTokens()
```
I plan to wait for 1 HHVM release and then remove optional &$cas_token and &$cas_tokens parameters from corresponding reffy functions.
The reason for splitting these functions off: extension implementation sends different option to memcached server depending on whether $cas_token was passed in or not.
Reviewed By: billf
Differential Revision:
D17139942
fbshipit-source-id:
b149050ce54a0e4dfaf4e62edff1d54333b581b5