More assert checks on reinsert breakpoint

More assert checks on reinsert breakpoint

This patch adds more asserts, so the incorrect or sub-optimal
reinsert breakpoints manipulations (from the tests in the following
patches) can trigger them.

gdb/gdbserver:

2016-06-17  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (linux_resume_one_lwp_throw): Assert
	has_reinsert_breakpoints returns false.
	* mem-break.c (delete_disabled_breakpoints): Assert
	bp type isn't reinsert_breakpoint.