only variables, and add a commented example in default.vcl.

The reason for this is to avoid VM write-backs to cached objects by default.

Previously we did this with the obj_readonly parameter, but this puts
it right where the user can see it.

Notice that the two variables are not locked, so they cannot be
trusted to be precise.

obj.lastuse changes to obj.last_use because its type changes from
DURATION to TIME, (and to improve readability in general)

Fix & Polish relevant test-cases

You have to be careful when you use them though: They compare strings.

bits into "feature" and "debug" flags.

Feature +esi_ignore_https treats it as http://... instead.

Default is "safe" in order to not expose any data by accident.

Fixes #1333

against the busy-list.

Fixes #1342

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.

state engine a bit while here.

Add author information to some files with significant changes.

VCL type, we can simplify the VCC backend code somewhat.

VCL created simple directors.

pass, it will be anyway.

Fixes #1335

The only real trouble was purges, and they now have their own vcl_purge{}

Sorry for the detour...

(Don't tell me nothing good ever comes from DB's delayed trains...)