Finish ReginaREXX port as IBM Classic REXX replacement

[prokushev]

Regina REXX is mostly working under OS/2. Originally, it had only 32-bit API functions
available. Recently, we mostly created proper 16-bit wrappers for 32-bit API's, plus
32-bit wrappers for 16-bit subcommand handlers (which are created by CMD.EXE
and 16-bit WPS functions). So, we now have mostly working 16-bit functions in CMD.EXE.
Also, sharing the REXX interpreter between different processes is now working too.
(originally, we were able to run a single REXX program at the same time, only. Now
this problem is fixed too.). We created our versions of REXX.DLL and REXXAPI.DLL
for that purpose, and they are mostly working.

Also, our current REXX.DLL and REXXAPI.DLL can be used as a "REXX switcher" for
different REXX interpreters. This works with renaming original interpreters to e.g.,

REXO.DLL and REXOAPI.DLL for Object REXX

and

REXC.DLL and REXCAPI.DLL for Classic REXX

with renmodul.exe utility form Hobbes. Then we'll be able to switch REXX interpreters
with setting environment variables. If we set

set REXX_DLL=REGINA
set REXXAPI_DLL=REGINA

then we'll have REGINA.DLL as our REXX interpreter. If we set

set REXX_DLL=REXC
set REXXAPI_DLL=REXCAPI

then we'll have Classic REXX interpreter loaded. So, we'll use REXC.DLL as our REXX.DLL
and REXCAPI.DLL instead of REXXAPI.DLL. The same with Object REXX. It is possible to
switch REXX interpreters on the fly this way, so. I'm able to have three different REXX
interpreters in three different CMD.EXE windows.

Though, currently, there are still some problems remained, which prevent to use
Regina REXX as a drop-in replacement for IBM Classic REXX

1. There are some minor syntax incompatibilities

2. Regina REXX has macrospace functions missing (actually, only dummy
   functions are present)

3. REXX queues implementation is a bit different from IBM's REXX queues. There
   are several types of queues (internal and external). IBM REXX interpreter has queues
   implemented in REXXAPI.DLL externally to the REXX interpreter. For REXX queues to
   behave IBM's way, we need to clone IBM's way of working with REXX queues in REXXAPI.DLL.

Currently, implementation of REXX queues and macrospace functions the IBM way is
in progress. Missing these parts will prevent us from running REXX extensions like
VXREXX and programs written on VXREXX (like Arca Noae package manager, for example).
So, we need this for sure for having Regina REXX as a drop-in replacement of IBM's
Classic REXX.

So, the current task is to finish Regina as a drop-in replacement