clib2 Code

- Changed how error conditions raised by dos.library file I/O functions
are detected.

- Modified function return values of 0 and -1 to use macros like OK,
ERROR/SEEK_ERROR instead, to better convey what the purpose of these
values is.

- Reversed the change in rename() which enforced deletion of the target file.

- The Unix-like rename() now removes the target file even if that
file has been protected from deletion.

- Added the two release archive build scripts.

- Fixed the startup build target directory names.

- Changed how the startup code is built for the different library flavours,
and which files this involves.

- Final version bump before release.

- Added a hopefully enlightening comment on the subtleties of semaphore
locking in the stdio_fflush.c file.

- The stdio locking in fcntl() wasn't working correctly. Fixed.

- Made the clearerr(), feof() and ferror() macros thread-safe.

- Small tweaks to fix GCC 68k compiler warnings.