<rdar://problem/13265017>

The notion of Crossref command has long been forgotten, and there is nothing using CommandObjectCrossref in the current LLDB codebase
However, this was causing a conflict with process plugins and command aliases ending up in an infinite loop under situations such as:
(lldb) command alias monitor process plugin packet monitor
(lldb) process att -n Calendar
Process 28709 stopped
Executable module set to "/Applications/Calendar.app/Contents/MacOS/Calendar".
Architecture set to: x86_64-apple-macosx.
(lldb) command alias monitor process plugin packet monitor

This fixes the loop (and consequent crash) by disposing of Crossref commands and related code

llvm-svn: 175831