Reintroduce PRIV_REQ as PRIV_TASK. PRIV_TASK is available (as separate priv pointers) both in the client side and the backend side VCL functions.

Make the VRTPRIV_* interface slightly more generic to let us use it without needing a req/sess pointer.

For now it probably only works with things like STRING and REAL.

thread pointer-ref, and deref it on thread scheduling failure.

The code tried to deref the same pointer twice, which failed because
the VBO_DerefBusyobj() will clear the pointer when called. Separating
allows calling VBO_DerefBusyobj() for each of them.

Fixes: #1628

backslash is used for escaping in varnish-cli, so escape the backslash
to actually pass "\.png$".

Minor cosmetic changes while here. Discussed with Dag on Frankfurt.

Move explanation to its own section. Also mention the state options.

Because -0 == +0, the use of negative numbers as a distinction between
hits and misses in the recorded bucket history fails when there are
entries of index 0.

Fixes: #1623

Added two counters to VBE.
conn: concurrent connections to backend.
req: number requests sent to backend.

With this is possible to find out whether the request was a pass (or
hit-for-pass) in a single place.

This had the same effect as writing to beresp.uncacheble.

abandonned us.

Fixes	#1624

I'm not sure how valuable this test is but put it in the right place
until it's decided.

Fixes #1616