Document the new return(retry).

Backend restarts are now return(retry).

Fixes:	#1503
Purge has changed.
Non-breaking space broke the control sequence.
Add a VXID() macro to strip client/backend bit from VXIDs.
Add VSL_End() function to make closedown of cached VSLs consistent
Add VSL_ChgId() to do the VSL dance and song for restart/retry
Improve args to VXID_Get()
Add some missing housekeeping for pipe
Strip marker bits from vxids
Move some args from busyobj to vfp_ctx
Put the struct body in vfp_ctx
I accidentally duplicated this SLT_Link yesterday.
We have a number of weird session error cases that still fail
out here and need a SLT_End record.
Give the CLI command vcl.show a -v flag which outputs all the source
files involved in a given VCL.

When using -v, the individual source files are output like this:

	// VCL.SHOW %d %d %s\n%s\n

First field is the source file index [0...].
Second field is the number of bytes in the source file.
Third field is the name of the source file.
Fourth field is the source file content.

Inspired by a patch from daghf
Un-copy&paste leading whitespace in test-cases
White space copy&paste fixups
White-space copy&paste fixups
Update from FreeBSD's sys/queue.h
Make it possible to return synth from vcl_deliver{}

This is now possible because synth responses do not go through
deliver any more, as error responses used to.

Patch by:	Nils Goroll

Much appreciated
Add a VCC variable type "HTTP" to refer to an entire
HTTP message.  Presently supported "req", "bereq", "resp", "beresp".