Implement UI controls.  Current controls are the possibility to output
the OpenSSL error stack on the same channel from within UI_process()
and to check if the same user interface can be redone without being
rebuilt (this is often more a question of philosophy than
technicalities).

well.

This probably requires reference counters and locks as well.  To be
implemented later.

prompting, application-defined prompts, the possibility to use
defaults (for example default passwords from somewhere else) and
interrupts/cancelations.

(for new functions...).  One might still want to be able to pass down
a user-data pointer to be used by the UI.  However, ex_data doesn't
quite cut it, since that means the appropriate index to it might need
to be shared between parts that aren't really related in that sense,
and would require the currently hidden (static) index holders to be
uncovered.  Not a good thing.  Therefore, add the possibility to add a
user-data pointer to a UI.

like des_read_password and friends (backward compatibility functions
using this new API are provided).  The purpose is to remove prompting
functions from the DES code section as well as provide for prompting
through dialog boxes in a window system and the like.

missed any.

This compiles and runs on Linux, and external applications have no
problems with it.  The definite test will be to build this on VMS.

them for a short period of time (actually, poll them with select(),
then read() whatever is there), which is about 10ms (hard-coded value)
each.

Separate Windows and Unixly code, and start on a VMS variant that
currently just returns 0.

Avoid enabled 'assert()' in production library.

used anywhere in OpenSSL, but might be used by libdes applications.

Never use des_set_key (it depends on the global variable des_check_key),
but usually des_set_key_unchecked.
Only destest.c bothered to look at the return values of des_set_key,
but it did not set des_check_key -- if it had done so,
most checks would have failed because of wrong parity and
because of weak keys.

(meaning pointer to char) to des_cblock * (meaning pointer to
array with 8 char elements), which allows the compiler to
do more typechecking.  (The changed argument types were of type
des_cblock * back in SSLeay, and a lot of ugly casts were
used then to turn them into pointers to elements; but it can be
done without those casts.)

Introduce new type const_des_cblock -- before, the pointers rather
than the elements pointed to were declared const, and for
some reason gcc did not complain about this (but some other
compilers did).