SSL option

Hi Adam,

I've been reviewing SSL code in pgAdmin3 and libpq7.4 for win32 (and got
it running with several patches). I added a compile time option to
reflect SSL availability, it needs the compile time flag -DSSL, which I
added to acinclude.m4.

We should have this configurable, in case a libpq is compiled without
openssl (without -lssl and -lcrypto). Best way would be if it was
possible to examine libpq if it's ssl enabled or not(compiled with
USE_SSL), I don't know if this is possible. Otherwise, we'd need
--with-openssl.

Regards,
Andreas