HPCC-11522 libmemcached plugin

Signed-off-by: jamienoss <james.noss@lexisnexis.com>
The "harm" is in confusing the user.  They read the documentation and see 3 functions - 
setInteger4, setInteger8 and setInteger - which one do I call?
And then having given them two different integer sizes it gives them scope to call the wrong one to get the result.
It also make it trivially harder to maintain.