clib2 Code

- Added another function called __reset_max_mem_stats() which will reset the
counters for "maximum amount of memory used" and "maximum number of chunks
allocated" to the current figures for these values.

- Fixed the alloca() declaration in <stdlib.h> so that software which keys
off the fact whether or not the alloca preprocessor symbol is defined
will do the right thing.

- Added an optional call-back function which can be called if alloca()
is about to return NULL, which some software does not consider.
Rather than letting such software drop into an illegal memory access
or worse, that call-back function will be invoked instead, which can
print an error message and eventually call abort().

- Fixed the header files I broke by mistake.

- You can now request that your program uses the clib2 alloca() function
rather than the built-in compiler alloca().

- alloca() is now part of libunix.a, too.

- Added notes on where to find documentation and updates to each header file.

- In libunix.a malloc(), calloc() and realloc() no longer treat a
request to allocate 0 bytes as an error, returning NULL. They all
return a pointer sized memory chunk (= four bytes) initialized to
NULL (= 0) instead.

- The alloca() implementation which allocates memory from the system
rather than the local stack frame is thread-safe now. It also
interacts with the realloc(), calloc(), free() and malloc() functions
in that the alloca() cleanup routine is called once alloca() has
done its job. If all the memory allocated through alloca() has been
released no further calls to the cleanup function will be made.

- In the thread-safe library, realloc() permitted two different overlapping
calls to succeed in trying to reallocate the same chunk of memory due to
a race condition. Fixed.

- Moved the thread-safe library documentation.

- The malloc() in libunix.a now allocates four bytes of memory instead
of just one for a request to allocate 0 bytes.

- Corrected the section numbering.

- Fixed the remaining HTML errors.

- Changed the assertion message text shown in the requester window.

- The standard malloc() now sets errno to EINVAL for zero length
allocations.

- Updated the general documentation and started to document the implementation-specific
behaviour of the library functions.

- In libunix.a malloc(), calloc() and realloc() no longer treat a
request to allocate 0 bytes as an error, returning NULL. They all
return a 1 byte memory chunk initialized to 0 instead.