lldb-server: add support for binary memory reads

Summary:
This commit adds support for binary memory reads ($x) to lldb-server. It also removes the "0x"
prefix from the $x client packet, to make it more compatible with the old $m packet. This allows
us to use almost the same code for handling both packet types. I have verified that debugserver
correctly handles $x packets even without the leading "0x". I have added a test which verifies
that the stub returns the same memory contents for both kinds of memory reads ($x and $m).

Reviewers: tberghammer, jasonmolenda

Subscribers: iancottrell, lldb-commits

Differential Revision: http://reviews.llvm.org/D13695

llvm-svn: 250295