openssl.c: make damn sure e_os.h knows about OPENSSL_C

(Should we point to snapshots, or directly give the one-line patch?)

I hope all memory leaks that may occur here have already been tracked down.

that is actually used (even though it may not appear so at first
sight).

This was meant for building individual ciphers separately;
but nothing of this is maintained, it does not work
because we rely on central configuration by the Configure
utility with <openssl/opensslconf.h> etc., so the files
are only wasting space and time.

lib$-functions and sys$-functions.

in addition to the crypto library.

"openssl list-standard-commands".

In testss, use MD5 as digest algorithm so that the resulting
certificates can be used for testssl with RSA.

in SSL_new.
If SSL_OP_SINGLE_DH_USE is set, don't waste time in SSL_[CTX_]set_tmp_dh
on computing a DH key that will be ignored anyway.

ssltest -dhe1024dsa (w/ 160-bit sub-prime) had an unfair performance
advantage over -dhe1024 (safe prime): SSL_OP_SINGLE_DH_USE was
effectively always enabled because SSL_new ignored the DH key set in
the SSL_CTX.  Now -dhe1024 takes the server only about twice as long
as -dhe1024dsa instead of three times as long (for 1024 bit RSA
with 1024 bit DH).

choice of parameters) when they are needed.