[fpc-pascal] Get user ID for name on Linux

[Marco van de Voort]

In our previous episode, geneb said:
> 
> > Many thanks! That's great. The completeness of FPC units and packages is really
> > astonishing.
> >
> Is there a complete list of packages available somewhere?

There is some info(1) in the wiki, though many details are missing, and the
status of each package is not explicitely recorded.

There however is a page specific about the libc_unit (2) that named the
 "users" package as a replacement for certain calls.

(1) http://wiki.freepascal.org/Package_List
(2) http://wiki.freepascal.org/libc_unit