NAME
        Open -- Open a file for input or output

    SYNOPSIS
        file = Open( name, accessMode )
        D0           D1    D2

        bptr open(strptr, long)

    FUNCTION
        The named file is opened and a file handle returned.  If the
        accessMode is MODE_OLDFILE, an existing file is opened for reading
        or writing. If the value is MODE_NEWFILE, a new file is created for
        writing. MODE_READWRITE opens a file with an shared lock, but
        creates it if it didn't exist.  Open types are documented in the
        <dos/dos.h> or <libraries/dos.h> include file.

        The 'name' can be a filename (optionally prefaced by a device
        name), a simple device such as NIL:, a window specification such as
        CON: or RAW: followed by window parameters, or "*", representing the
        current window.  Note that as of V36, "*" is obsolete, and CONSOLE:
        should be used instead.

        If the file cannot be opened for any reason, the value returned
        will be zero, and a secondary error code will be available by
        calling the routine ioerr().

    INPUTS
        name       - pointer to a null-terminated string
        accessMode - integer

    RESULTS
        file - BCPL pointer to a file handle

    SEE ALSO
        close(), changemode(), namefromfh(), parentoffh(), examinefh()