Bump minimum libmemcached to 1.0.2

1.0.2 was released 20 months ago, get rid of several code #ifdefs by
requiring a minimum version of that.
Switch to newer post-1.0 libmemcached data types

Until now we were relying on libmemcacehd deprecated types that they
were supported via an internal typedef mechanism. Now that we only
support >= 1.0.2, use the newer API.