Add Vim frontend to LLDB.

Add Vim frontend to LLDB.
- Access any LLDB CLI command in Vim by typing ":L<command>". Tab-completion
  works too!
- See source locations for breakpoints and the current PC with vim "marks"
  and highlights.
- Examine backtraces, locals, disassembly, registers, and breakpoints in
  dedicated Vim windows.
- See when in-scope variables and registers change by watching for (red)
  highlights.

This plugin opens multiple Vim "windows" to display debugger information.
To quit all windows at the same time use ":qa". The alternative would be
":q" to close each window separately.

This plugin is known to work on Mac OS X (Mountain Lion) with MacVim and
the system-provided terminal Vim, and on Linux (Ubuntu 12.04 and 12.10)
with GVim and the terminal Vim from the "vim-gnome" package.

llvm-svn: 174892