autoconf madness

[Nils Goroll]

> Now for reasons which I do not understand, autoconf seems to create an
> environment where the second (inner) configure called via make distcheck gets
> passed the CFLAGS determined during the first (outer) configure run.

Today I've changed configure.ac and Makefile.am to save the external CFLAGS and
explicitly pass them to the inner configure explicitly (commits
cb00896414ba72c7cc10882c1be7e23dfb796dd3 and
d49afc041773f915e74a82c962063edde3e1d9eb).

This feels like a workaround to me, in particular because CFLAGS is just one of
many relevant environment variables which we touch. IMHO, a good solution would
restore all of the original environment for distcheck.

Any ideas?

Nils