<rdar://problem/14717184>

Improve the documentation for the new target.memory-module-load-level setting, and also return an error when there is no nlist data when appropriate.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@188317 91177308-0d34-0410-b5e6-96231b3b80d8