Allocate bpstats with new

Allocate bpstats with new

This changes struct bpstats to be allocated with new and freed with
delete, adding constructors and a destructor in the process.  This
allows the removal of one cleanup and clears the way for more to
follow.

gdb/ChangeLog
2017-09-20  Tom Tromey  <tom@tromey.com>

	* breakpoint.c (~bpstats): Rename from bpstat_free.  Update.
	(bpstat_clear): Use delete.
	(bpstats): New constructors.
	(bpstat_copy, bpstat_stop_status): Use new.
	(dprintf_after_condition_true): Update.
	* breakpoint.h (bpstats::bpstats): Add constructors.
	(bpstats::~bpstats): Add destructor.