HPCC-12728 The memcached plugin does not compiling on Ubuntu 12.04

Because the version of libmemcached headers is too old.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
indent looks correct to me. We never indent #if statements (well, sometimes we do when nesting them) and we leave the indent of the controlled C++ code matching what it should be after preprocessing.