Fixes: #1610

Improve consistency, add argument names and rewording.

Spotted by: coredump

Try to avoid confusing everyone, since "4.0.1" (really trunk) has
fresher data than 4.0.2 (proper 4.0).

Mostly important for the sphinx builds put online.

Writing to bereq.uncacheable in backend_response and backend_error would only
make sense in the context of a retry. In most real world cases, writing to
be*resp*.uncacheable would be intended in backend_response and backend_error.

dot -Tpdf seems to work fine

Noted by:	Matt Robenolt

This was mentioned in the user guide, but not in the man
page itself.

Pointed out by:		Brett Fitzgerald

Submitted by: Martin Clausen <martclau@gmail.com>

Implement -k argument in vut for use with varnishlog. This takes as an
argument the number of log transactions to be processed before
exiting. Useful to stop varnishlog after a given set of log data has
been produced.

Drop -s from the 'not implemented yet' list as this option has very
limited usefullness.

Submitted by:	fgs

might have, it doesn't make any sense.

Fixes	#1602