Prevent clear_command from directly modifying breakpoint list.

	Prevent clear_command from directly modifying breakpoint list.
	* Makefile.in (breakpoint_h): Update dependency.
	* breakpoint.c (clear_command): Do not remove
	breakpoints from breakpoint_chain.  Collect breakpoints
	to delete in a vector.
	* breakpoint.h (breakpoint_p): New typedef for pointer to
	breakpoint.  Register vector of breakpoint_p.