MFC r210679:

MFC r210679:
Report the time left for the sleep on SIGINFO.
Be stricter in the checking of interval specification.

MFC r210696:
Deal with proper format for printing time_t.

MFC r210749:
Simplify argument parser by using sscanf(); simplify usage() by not
refusing to use stdio.
Reduce nesting level in the sleep loop by returning earlier for negative
timeouts.
Limit the maximum timeout to INT_MAX seconds.

MFC r210750:
Document the new argument parser for sleep(1) and SIGINFO behaviour.
Remove higlight for the unportability notice.

git-svn-id: svn://svn.freebsd.org/base/stable/8@211536 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f