Fixes #1546

Fixes: #1591

Fixes: #1592

Require that buffer arguments have greater than zero length to allow
for zero termination.

Make sure that NULL buffers are not touched.

Spotted by:	Dridi Boukelmoune

Use vcl_synth or vcl_backend_error where appropriate.

For master we retain the more strict check in case we forget to bump
the API version as discussed on irc.  Implementation idea from scoof.

Fixes #1538

Not being able to fchown() is normal when running varnishd
unprivileged, so don't report failure unless running as root.

Add missing braces, avoid unnecessary variables.

Noticed by:	fgs

Extensive test cases often lead to a lot of log output,
which at times tripped the following assert:

Assert error in vtc_log_emit(), vtc_log.c line 122:
  Condition(vtclog_left > l) not true.

Double the amount of buffer space allowed to avoid this. Another 256KB
memory use per concurrent running test should be fine.

Requests that end up in the hard "400 Bad Request" handling used to be
logged with incomplete data. (no method, maybe no path, possibly no proto,
and no response status)

Port scans or anything sending a byte and a linefeed would be logged.

Since this is used for logging access to a web site, it makes more sense
to skip these garbage requests.

Fixes:		#1584

Adding a dash if missing the path component does not make sense.

Related bug:	#1584

child process during startup.

Fixes #1407

This prevents SLT_ReqAcct log records with 0 as VXID.

non-fatal.

Fixes: #1414

Fixes: #1466

Fixes #1580

Fixes #1583

Fixes a regression from 33e6fe71

Fixes #1585