Description:
------------
When performing a get with a cas token requested a multi-get is performed 
internally.  After doing so 
only the first result is fetched, leaving the final RES_END result on the stack.  
As per the 
libmemcached documentation memcached_fetch_result should be called until it 
returns NULL following a 
multi-get.

In some circumstances this is not noticeable as libmemcached takes care of 
flushing the receive buffers 
accordingly, however certain subsequent operations will incorrectly return the 
left-over RES_END result.  
I have seen this behaviour exhibited when performing a get with cas token 
request followed by an add 
operation though there may be other examples.

I have tested this with memcached extension version 2.0.0b2 using libmemcached 
0.53 and 1.0.2, though I 
believe the issue also exists with earlier versions.

Please find attached a patch against 2.0.0b2 to address this issue which both 
resolves the primary issue 
and also simplifies the call in the case that a cas token is not required  by 
calling 
memcached_get_by_key.

Please let me know if I've been unclear!