configure bug

[Chris J. Herbst]

This was dicovered in openssh-2.9p2 on BSDi 4.1.  If you configure
--with-ssl-dir and give a relative path (like ../openssl-0.9.6b), it will
not compile because that path is no longer valid once it cds to
openbsd-compat.  In the CPPFLAGS variable in openbsd-compat/Makefile, you
can put in another ../ (-I../openssl-0.9.6a/include becomes
-I../../openssl-0.9.6a/include) and it works.

Perhaps there should be some warning about configuring with a relative
path, or perhaps configure can convert to an absolute path, or even
better, make sure the relative path in openbsd-compat/Makefile is still
valid.