procedure computes the full path name of
the executable file from which the application was invoked and saves
it for Tcl's internal use.
The executable's path name is needed for several purposes in
Tcl.  For example, it is needed on some platforms in the
implementation of the <B><A HREF="../TclCmd/load.html">load</A></B> command.
It is also returned by the <B><A HREF="../TclCmd/info.html">info nameofexecutable</A></B> command.
<P>
On UNIX platforms this procedure is typically invoked as the very
first thing