* systime.h: Doc fix.

* systime.h: Doc fix.
	(EMACS_SET_USECS): Remember that a `usec' is a microsecond, not a
	millisecond.  What's three orders of magnitude between friends?
	* dispnew.c (Fsit_for, Fsleep_for): Remember to multiply the
	`milliseconds' argument by 1000 to get microseconds.

	* dispnew.c (Fsleep_for, Fsit_for): Allow SECONDS to be a
	floating point value.

	* dispnew.c (getenv): Extern declaration deleted; this is done in
	config.h.