clib2 Code

- 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.

- reverted the soft-float subdirectory changes as the problem was solved by
olaf in a different way so that libm.a never contains any hard float
opcodes and instead libm881 contains them. so the separate soft-float
directory are not required.

[tboeckel]: when compiling amiga_rexxvars.c for m68k/OS3 the GetRexxVarFromMsg()
and SetRexxVarFromMsg() will not be used and therefore not cause linkage errors
with our libamiga.a stubs anymore.