* sol-thread.c: More cleanup, add comments.

	* sol-thread.c:  More cleanup, add comments.
	* (sol_thread_resume):  Prevent people from trying to step
	inactive threads.
	* (sol_thread_wait sol_thread_fetch_registers
	sol_thread_store_registers):  Remove unnecessary check for
	sol_thread_active.  These routines won't get called unless threads
	are active.