Now that directors are in VMODs and VCL_BACKEND is a bona fide
VCL type, we can simplify the VCC backend code somewhat.
Update copyright notices in preparation for release
Remove counters related to DNS director.
Count the number of times a threadpool runs against the upper limit
Add author to libvarnishapi files

Add author information to some files with significant changes.
Update copyright dates in various files
Add missing copyright header and author information
Add copyright and license information to devicedetect.vcl
moving on:  Pass the IMS candidate objcore to VBF and polish its
state engine a bit while here.
Update copyright
Add the skeleton of a Conditional Fetch facility.

This comes with a big apology to Geoff Simmons:  I should have
tackled Conditional Fetch before even thinking about streaming
and therefore this has taken much longer than it should.
Trivial test-case for conditional fetch