clib2 Code

- Added 68k stubs to amiga_rexxvars.c for the OS4 build to use. The new code now
works just about exactly like the amiga.lib RVI code used to do, which means
that there is no artificial length limit for the number of characters a string
retrieved may have, and the code is largely reentrant.

- The 68k stub for StrcpyN stored d1 as a result value, which was both
dangerous and unnecessary.

- Plugged in 68k stubs for the OS4 build.

- To work around a bug in the Roadshow TCP/IP stack (since fixed), the waitselect()
function now substitutes a 10 microsecond timeout for a zero length timeout.

- isatty() now checks if the file descriptor refers to a real file before
it calls IsInteractive() on it.

- Added disk type definitions to mount_convertinfo.c and unistd_common_pathconf.c,
prompted by Thore Boeckelmann.

- Preparations for OS4 conversion.

- MakeString() did not clear the ns->ns_Ivalue field and did not NUL-terminate
the copied string either. Fixed.

- Small indentation changes for the stub code.

- Rewrote the GetRexxVar()/SetRexxVar() functions (mostly) in 'C', using available
code as a reference. The 68k stubs currently only work for the 68k version of
the library, and a solution for the OS4 build still needs to be found. The code
is currently untested, but it should be complete.

- Added local inline function definitions for the two rexxsyslib.library V45
API functions, rather than omitting support for them in the 68k build.