Various fixes mostly relating to the User Settings stuff:

- Added new utility function to Arg, GetQuotedCommandString, which re-assembles
the args into a string, replacing quotes that were originally there.

- Modified user settings stuff to always show individual elements when printing out
arrays and dictionaries.

- Added more extensive help to 'settings set', explaining more about dictionaries
and arrays (including current dictionary syntax).

- Fixed bug in user settings  where quotes were being stripped and lost, so that
sometimes array or dictionary elements that ought to have been a single element
were being split up.

llvm-svn: 121438