Appion

I ran into this when writing a 3D file using the same code and then reading it into PyMOL. PyMOL rejects the file as not being an MRC file because of the missing 'MAP ' string.

source:trunk/programs/ace2/MRC.m#L224

When ACE2 writes the MRC header it sets four-byte 53 to 0, when it should equal 'MAP '. Documentation here: http://emg.nysbc.org/software/mrctools/mrc_specification.php

Old code:

    header->map            = 0;

Suggested replacement:

    // "MAP " from ascii to little-endian integer:  
    //   ord('M')=77, ord('A')=65, ord('P')=80, ord(' ')=32
    //   reverse order and powers of 256
    //   32*(256**3) + 80*(256**2) + 65*(256) + 77
    header->map            = 542130509;

I have fixed and tested the code, but I do not want to commit until given approval, because of the code freeze.