Added a speed test to the GDBRemoteCommunicationClient and

GDBRemoteCommunicationServer classes. This involved adding a new packet
named "qSpeedTest" which can test the speed of a packet send/response pairs
using a wide variety of send/recv packet sizes.

Added a few new connection classes: one for shared memory, and one for using
mach messages (Apple only). The mach message stuff is experimental and not 
working yet, but added so I don't lose the code. The shared memory stuff
uses pretty standard calls to setup shared memory.

llvm-svn: 128837