Can't read mmCIF with lowercase cartn_x field name

[Tom Goddard]

I got an mmcif file written by Coot that used _atom_site.cartn_x as a field name that ChimeraX could not read giving the error that there was no _atom_site.Cartn_x. I guess it is expecting uppercase C while the file had lower case c. Supposedly the mmCIF spec says the names are case insensitive.

I'm not going to attach the mmCIF file since it is very large, 60 Mbytes, but it is easy to test by editing any mmCIF.

[Tom Goddard]

This mmcif syntax web page

​http://mmcif.wwpdb.org/docs/tutorials/mechanics/pdbx-mmcif-syntax.html

says

"Data category and data item names are not case sensitive."

[Greg Couch]

Modified readcif code to treat category tags as case insensitive.

[pett]

reducing # of categories, so lumping into I/O category