clib2 Code

- The types of the __default_path_delimiter and __default_path variables
were wrong.

- Rewrote execve() from scratch and documented it.

- The default configuration options for execvp() are now configurable at
link time.

- Added the exec() family functions to the makefiles and the <unistd.h>
header file.

- Added preliminary versions of the exec() family functions.

- Added the missing string pointer.

- Added pathconf() and fpathconf() as contributed by Peter Bengtsson. Thank you very much!

- Added sysinfo() as contributed by Peter Bengtsson. Thank you very much!

- Added ftime(), ulimit(), getrlimit() and setrlimit() as contributed by
Peter Bengtsson. Thank you very much!

- Added ftime(), as contributed by Peter Bengtsson. Thank you very much!

- Added the missing S_ISSOCKET() macro to <sys/stat.h>. Note that this
is not actually a POSIX feature.

- Added fmin(), fminf(), fmax() and fmaxf() to the build makefiles.
Somehow I must have forgotten about them :-(