Followup check in for http://llvm.org/viewvc/llvm-project?rev=148491&view=rev,

where we changed the CommandObjectSettingsSet object impl to require raw command string.

Do the same for CommandObjectSettingsReplace class and add two test cases; one for
the "settings replace" command and the other to ensure that completion for variable
name still works. 

llvm-svn: 148615