Pass VMOD_DIR to make distcheck
Pass VMOD_DIR to make distcheck

The VMOD_DIR returned from pkg-config does not take prefix and similar
variables into account. Make sure to pass an explicit VMOD_DIR that
the build process has write access to.

Fixes #8

Conflicts:
	Makefile.am

varnish/libvmod-softpurge,varnish/libvmod-softpurge