Patch for review: target modules show-unwind errors

When using the “target modules show-unwind”, it was very difficult to tell whether I had typed something wrong or it had found zero results.

All of these commands would return nothing:
target modules show-unwind 0x80484d0 ; invalid command - nothing done
target modules show-unwind -a 0x80484d0 ; this is a valid command that
target modules show-unwind -foobar 0x80484d0 ; invalid command - nothing done

target modules show-unwind nonexistentfunctionname ; invalid command - nothing done

The patch below returns an error string if you specify an invalid option, don’t specify an option, or no results were found.

Please let me know if it’s ok to submit. Thanks.
-Mike

mikesart@mikesart-rad:~/data/src/llvm.svn/llvm/tools/lldb$ svn diff
Index: source/Commands/CommandObjectTarget.cpp

Looks good, thanks for making the fix. Please commit the patch.

(forgot to Cc the list on my orig reply)