ENGINE code does not return a default, set an error.

Previously RAND_get_rand_method was returning a non-const pointer, but it
should be const. As with all other such cases, METHOD pointers are stored and
returned as "const". The only methods one should be able to alter are methods
"local" to the relevant code, in which case a non-const handle to the methods
should already exist.

This change has been forced by the constifying of the ENGINE code (before
which RAND_METHOD was the only method pointer in an ENGINE structure that was
not constant).

At the same time, add VMS support for Rijndael.

instead of 'unsigned' counters.
Seed PRNG in MacOS/GetHTTPS.src/GetHTTPS.cpp.

Partially submitted by Yoram Meroz <yoram@mail.idrive.com>.

are not guaranteed to be unpredictable.

returns int (1 = ok, 0 = not seeded). New function RAND_add() is the
same as RAND_seed() but takes an estimate of the entropy as an additional
argument.

This will soon be complemented with MacOS specific source code files and
INSTALL.MacOS.

I (Andy) have decided to get rid of a number of #include <sys/types.h>.
I've verified it's ok (both by examining /usr/include/*.h and compiling)
on a number of Unix platforms. Unfortunately I don't have Windows box
to verify this on. I really appreciate if somebody could try to compile
it and contact me a.s.a.p. in case a problem occurs.

Submitted by: Roy Wood <roy@centricsystems.ca>
Reviewed by: Andy Polyakov <appro@fy.chalmers.se>

Submitted by:
Reviewed by:
PR: