Fix PR gdb/19187 (process record over a fork causes internal error)

Fix PR gdb/19187 (process record over a fork causes internal error)

Right after a fork is detected, we detach breakpoints from the child
(detach_breakpoints), which calls into target_remove_breakpoint with
inferior_ptid pointing at the child process, but leaves the breakpoint
marked inserted (in the parent).

The problem is that record-full.c always deletes all knowledge of the
breakpoint.  Then when we later really delete the breakpoint from the
parent, we fail the assertion, since the breakpoint is unexpectedly
not found in the record-full.c breakpoint table.

The fix is simply to not forget about the breakpoint if we're
detaching it from a fork child.

gdb/ChangeLog:
2016-08-10  Pedro Alves  <palves@redhat.com>

	PR gdb/19187
	* record-full.c (record_full_remove_breakpoint): Don't remove the
	breakpoint from the record_full_breakpoints VEC if we're detaching
	the breakpoint from a fork child.

gdb/testsuite/ChangeLog:
2016-08-10  Pedro Alves  <palves@redhat.com>

	PR gdb/19187
	* gdb.reverse/waitpid-reverse.exp: Add comment and remove
	setup_kfails.