for some early versions of re2.

Also get rid of an unnecessary #include "config.h".

Reduce code duplication for set.string() and .backend().

vcl.h must come before vrt.h for the VMOD event function typedef.

See Varnish issue #2449

space for task-scoped match data from workspace.

no longer using pthread keys.

the year.

it uncovered.

In 5.0, if strings enclosed in {"..."} had a newline, the newline
was apparently removed from the string, at least by the time it
was passed into a VMOD. This artificially causes some of the tests
in options.vtc to fail.

The problem was apparently fixed by Varnish 5.1. So this just comments
out the offending tests in options.vtc, they will be enforced in other
versions of the VMOD.