declare their own error strings so that they can be more easily compiled as
external shared-libraries if desired. Also, each implementation has been
given canonical "dynamic" support at the base of each file and is only
built if the ENGINE_DYNAMIC_SUPPORT symbol is defined.

Also, use "void" prototypes rather than empty prototypes in engine_int.h.

This does not yet;
  (i) remove error strings when unloading,
 (ii) remove the redundant ENGINE_R_*** codes (though ENGINE_F_*** codes
      have gone), or
(iii) provide any instructions on how to build shared-library ENGINEs or
      use them.

All are on their way.

NOTE: Boolean input hasn't been very well tested yet, so this part may
fail miserably.

success return, any negative number is a failure.  Make sure we check
the return value with that in mind.

  with arbitrary arguments instead of just a string.
- Change the key loaders to take a UI_METHOD instead of a callback
  function pointer.  NOTE: this breaks binary compatibility with
  earlier versions of OpenSSL [engine].
- Addapt the nCipher code for these new conditions and add a card
  insertion callback.

passwords that were given to the key loading functions were completely
ignored, at least in the ncipher code, and then we made the assumption
that the callback wanted a prompt as user argument.

All that is now changed, and the application author is forced to give
a callback function of type pem_callback_cb and possibly an argument
for it, just as for all other functions that want to generate password
prompting.

NOTE: this change creates binary and source incompatibilities with
previous versions of OpenSSL [engine].  It's worth it this time, to
get it right (or at least better and with a chance that it'll work).

appropriate code if any of them is defined.

This change adds some basic control commands to the existing ENGINEs
(except the software 'openssl' engine). All these engines currently load
shared-libraries for hardware APIs, so they've all been given "SO_PATH"
commands that will configure the chosen ENGINE to load its shared library
from the given path. Eg. by calling;
    ENGINE_ctrl_cmd_string(e, "SO_PATH", <path>, 0).

The nCipher 'chil' ENGINE has also had "FORK_CHECK" and "THREAD_LOCKING"
commands added so these settings could be handled via application-level
configuration rather than in application source code.

Changes to "openssl engine" to test and examine these control commands will
be made shortly. It will also provide the necessary tips to application
programs wanting to support these dynamic control commands.

The existing ENGINEs (including the default 'openssl' software engine) were
static, declared inside the source file for each engine implementation. The
reason this was not going boom was that all the ENGINEs had reference
counts that never hit zero (once linked into the internal list, each would
always have at least 1 lasting structural reference).

To fix this so it will stay standing when an "unload" function is added to
match ENGINE_load_builtin_engines(), the "constructor" functions for each
ENGINE implementation have been changed to dynamically allocate and
construct their own ENGINEs using API functions. The other benefit of this
is that no ENGINE implementation has to include the internal "engine_int.h"
header file any more.

ENGINE handler functions should take the ENGINE structure as a parameter -
this is because ENGINE structures can be copied, and like other
structure/method setups in OpenSSL, it should be possible for init(),
finish(), ctrl(), etc to adjust state inside the ENGINE structures rather
than globally. This commit includes the dependant changes in the ENGINE
implementations.

sure they are available in opensslconf.h, by giving them names starting
with "OPENSSL_" to avoid conflicts with other packages and by making
sure e_os2.h will cover all platform-specific cases together with
opensslconf.h.

I've checked fairly well that nothing breaks with this (apart from
external software that will adapt if they have used something like
NO_KRB5), but I can't guarantee it completely, so a review of this
change would be a good thing.

engine structure, and some ANSI C compilers will complain otherwise.

few small constifying changes, and why not throw in a couple of extras
while I'm at it?

At the same time, add VMS support for Rijndael.