NAME
        SetProgramDir -- Sets the directory returned by getprogramdir (v36)

   SYNOPSIS
        oldlock = SetProgramDir(lock)
        D0                       D1

        bptr setprogramdir(bptr)

   FUNCTION
        Sets a shared lock on the directory the program was loaded from.
        This can be used for a program to find data files, etc, that are
        stored with the program, or to find the program file itself.  NULL
        is a valid input.  This can be accessed via getprogramdir() or
        by using paths relative to PROGDIR:.

   INPUTS
        lock - A lock on the directory the current program was loaded from

   RESULT
        oldlock - The previous ProgramDir.

   SEE ALSO
        getprogramdir(), open()