posix.cfg: Added support for rewinddir().
Merge pull request #480 from orbitcowboy/master

posix.cfg: Added support for rewinddir().
Improve readability of Library::load()
by caching often used node names.

Also constify existing name caches.
Add mmap() / mmap64() / munmap() to posix.cfg. Enables basic leak tracking

Includes function prototype in posix.cfg as comment
for easier overview of the function arguments.