Add "target.process.stop-on-shared-library-events" setting, and make it work.
Add the ability to give breakpoints a "kind" string, and have the StopInfoBreakpoint
print that in the brief description if set.  Also print the kind - if set - in the breakpoint
listing.
Give kinds to a bunch of the internal breakpoints.
We were deleting the Mac OS X dynamic loader breakpoint as though the id we had stored away was
a breakpoint site ID, but in fact it was a breakpoint id, so we never actually deleted it.  Fixed that.