SSL on win32

Hello!

Here is a patch to fix win32 ssl builds. Summary of changes:

* Links with -leay32 and -lssleay32 instead of crypto and ssl. On win32,
"crypto and ssl" is only used for static linking.

* Initializes SSL in the backend and not just in the postmaster. We
cannot pass the SSL context from the postmaster through the parameter
file, because it contains function pointers.

* Split one error check in be-secure.c. Previously we could not tell
which of three calls actually failed. The previous code also returned
incorrect error messages if SSL_accept() failed - that function needs to
use SSL_get_error() on the return value, can't just use the error queue.

* Since the win32 implementation uses non-blocking sockets "behind the
scenes" in order to deliver signals correctly, implements a version of
SSL_accept() that can handle this. Also, add a wait function in case
SSL_read or SSL_write() needs more data.

I'd appreciate it if one of the win32 guys can confirm that this patch
fixes the build for them as well.

//Magnus