add option to mlockall memcached (was: Improve Swapping Behavior on OS X.)

Gentlefolk,

As a developer, I use the OS X build as my test platform. It runs on a quite large machine (4 3.4 GHz i7 SMT cores, 24 GB RAM, multiple disk spindles). When Couchbase is the only app running and has 13 GB out of 24 GB allocated to it, it claims to be using a large amount of swap. Other OS X diagnostic tools confirm its self-reported usage. On Linux, you recommend that we solve this problem by reducing the "swappiness" to 0. AFAIK, there is no equivalent on OS X. But there is wired memory. As I understand it, it is quite easy to use. Every OS emulator, VMware and Parallels, wire down their RAM and do not, as a result, suffer from OS X swapping out their memory. Please consider doing the same. It will really improve the situation as we push our test platforms under load.

Anon,
Andrew