Simplify sys_getloginclass.

Just use current thread credentials as they have the same accuracy as the
ones obtained from proc..
Reported by:	Coverity
CID:		1249760
Reviewed by:	neel
Approved by:	neel
Sponsored by:	QNAP Systems Inc.
Remove the distinction between strings and numbers from ctld(8) yacc parser.
This fixes problems with passing strings that look like numbers to clauses
that expect strings; previously it caused syntax errors and had to be worked
by user, using quotes.  The workaround introduced in r267833 is no longer
neccessary.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Improve compatibility with GNU timeout

According to the coreutils regression testsuite for timeout(1)
It is expect to exit with a status being:
125 in case an invalid duration or signal is passed in arguments
126 in case an invalid command is passed in arguments
127 in case the command passed in arguments does not exists.

While here document this behaviour in the man page
Fix build after previous commit.  While here, improve error messages.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Add regression tests for the timeout(1) utility

They are modeled over the regression tests that are provided for the GNU
coreutils timeout(1) utility