vtstor.c includes vtstor.h which includes vcc_if.h

This partly reverts c7087ebce9f035d436a9b215657a91e5a8463aed

I am aware that creating dependencies on vcc_if.h doesn't look as nice
as having a vcc target, but parallel builds just don't work otherwise

@fgsch is right, the additional path elements should not be needed

to be stored is NULL

the underlying hash, and getter methods return the config values

as is common for Varnish 4 VMODs, rather than against a source
directory, This necessitated using SHA256 for hashing rather then
CRC32, since vsha256.h is available in the "public" VRT, but not
vgz.h. For now, we just use the first 32 bits (MSB's) from the
SHA256 hash.

the Cookie headers of ESI-included requests.

- VMOD function vxid commented out, because 4.0.3 doesn't have PRIV_TASK
- VRT_selecthttp is also not exposed in 4.0.3