merge lldb-platform-work branch (and assorted fixes) into trunk

    Summary:
    This merge brings in the improved 'platform' command that knows how to
    interface with remote machines; that is, query OS/kernel information, push
    and pull files, run shell commands, etc... and implementation for the new
    communication packets that back that interface, at least on Darwin based
    operating systems via the POSIXPlatform class. Linux support is coming soon.

    Verified the test suite runs cleanly on Linux (x86_64), build OK on Mac OS
    X Mountain Lion.

    Additional improvements (not in the source SVN branch 'lldb-platform-work'):
    - cmake build scripts for lldb-platform
    - cleanup test suite
    - documentation stub for qPlatform_RunCommand
    - use log class instead of printf() directly
    - reverted work-in-progress-looking changes from test/types/TestAbstract.py that work towards running the test suite remotely.
    - add new logging category 'platform'

    Reviewers: Matt Kopec, Greg Clayton

    Review: http://llvm-reviews.chandlerc.com/D1493
Formatting.