Make the script work again from the command line as long as the PYTHONPATH

environment variable it set to include a path to lldb.py.

Also fixed the case where the executable can't be located and doesn't match
what is installed on the current system. It will still symbolicate the other
frames, and will just show what was originally in the crash log file.

Also removed the --crash-log option so the arguments to the "crashlog"
command are one or more paths to crash logs.

Fixed the script to "auto-install" itself when loaded from the embedded
script interpreter. Now you only need to import the module and the
command is ready for use.

llvm-svn: 148561