The reason is the same as for
https://github.com/varnishcache/varnish-cache/issues/2708 :

VRT_priv_task may now return NULL for out-of-workspace errors, see
https://github.com/varnishcache/varnish-cache/commit/de2b431086a13b243dc8b3e71cd8697db1df2c7f

- We write our own SYNOPSIS.
- Update Varnish version compatibility statement.
- Remove the reference to the pcre_* varnishd params in LIMITATIONS
  (no longer true).
- Spelling fix

We cannot access the varnishd params from a $ABI vrt vmod any more
and doing so does not appear a strong enough reason to change the $ABI.

Previously, pcre limits were taken from the varnish parameters
pcre_match_limit and pcre_match_limit_recursion, now they can be
defined on the re object or match level.

Otherwise parallel make distcheck fails

see varnish-cache aa8875a44d587bc5530554963f93fffba99efadd

vrt.h is included by cache.h and may not be included after it.

Because we don't copy the subject's terminating null byte, we can't use
strlen().

Fixes #4

and don't work around the previous off-by-one error in WS_Assert_Allocated
any more.
Fixes #3 for master.

This reverts commit bf2b7a78.

There are actually two off-by-one errors, one in WS_Assert_Allocated(),
and another in the use of -1 to have WS_Assert_Allocated() compute
the size of the string, including the null terminator.

We don't need the subject with the null terminator in the ov_t
structure (PRIV_TASK data), because we just need it to get backrefs
from the indices in the ov vector returned from pcre.

Also, there's a system in the VTC tests that may not be obvious.
The b*.vtc tests are about regex matching, c*.vtc for backrefs.

and add a test for it

Fixes #3

Closes #2

The .failed() and .error() methods have been removed.

The .match_dyn method has been removed, in its place we have the
functions match_dyn and backref_dyn.

Closes #1

for example if there was an error initializing the object.