Fix a mis-feature with propagation of breakpoint options -> location options.

When an option was set at on a location, I was just copying the whole option set 
to the location, and letting it shadow the breakpoint options.  That was wrong since
it meant changes to unrelated options on the breakpoint would no longer take on this
location.  I added a mask of set options and use that for option propagation.

I also added a "location" property to breakpoints, and added SBBreakpointLocation.{G,S}etCommandLineCommands
since I wanted to use them to write some more test cases.

<rdar://problem/24397798>

llvm-svn: 309772