Require recent autoconf.

On EL6 systems the packaged 2.63 version is missing AS_VAR_COPY.
This seems to have been added in 2.63b, released sometime in 2008.

With this commit we cut off any vmod development being done on
EL6 and earlier. (building and running should work)
Add more dependencies.

We need pkg-config and a new libvarnishapi to build, and varnishd to run
the test suite.

Conflicts:
	debian/control
Help confused dependency resolver on EL7.

Conflicts:
	vmod-curl.spec
Use correct unpack directory.

Conflicts:
	vmod-curl.spec
Import fresh version from libvmod-example.
Add /usr/sbin to path when looking for varnishd.
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
Adhere to libvmod-example standard file names.
Adhere to libvmod-example best practice.