NAME
        Lock -- Lock a directory or file

    SYNOPSIS
        lock  = Lock( name, accessMode )
        D0            D1        D2

        bptr lock(strptr, long)

    FUNCTION
        A filing system lock on the file or directory 'name' is returned if
        possible.

        If the accessMode is ACCESS_READ, the lock is a shared read lock;
        if the accessMode is ACCESS_WRITE then it is an exclusive write
        lock.  Do not use random values for mode.

        If Lock() fails (that is, if it cannot obtain a filing system lock
        on the file or directory) it returns a zero.

        Tricky assumptions about the internal format of a lock are unwise,
        as are any attempts to use the fl_Link or fl_Access fields.

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

    RESULTS
        lock - BCPL pointer to a lock

    SEE ALSO
        unlock(), duplock(), changemode(), namefromlock(), duplockfromfh()