updated posix library

[Luiz Henrique de Figueiredo <lhf@...>]

I've finally updated the POSIX library to Lua 5.0. It's available at
	http://www.tecgraf.puc-rio.br/~lhf/ftp/lua/lposix.tar.gz

Unlike the Lua code and my other Lua libraries, this one depends on the
operating system. I tried to follow the specifications in
	http://www.opengroup.org/onlinepubs/007904875/toc.htm
but not even recent Solaris follow them (for instance, they don't have
setenv and unsetenv). The other reference I have is the book
	Posix Programmer's Guide
	Writing Portable Unix Programs With the Posix. 1 Standard
	by Donald Lewine
My version is from 1994 and it differs from the online reference above in
several details.

I don't have access to many different systems to try this library on and so
I have to rely on the community to test it. Many systems claim to support POSIX
but they do so in different degrees. Please send me your reports about what is
missing in the library and what is missing in your system.

Thanks for your feedback. Enjoy.
--lhf