Make insert_breakpoints return void.

	Make insert_breakpoints return void.
	* breakpoint.h (insert_breakpoints): Change
	return type to void.
	* breakpoint.c (insert_breakpoints): Change
	return type to void.  Rename local return_val
	variable to error.
	* infrun.c (keep_going): Instead of checking
	return value from insert_breakpoints, catch exception.