Error near the end of tests about desimodel

[rainwoodman]

It is related to the fits table _tiles cached in the io module.

My astropy is too old (1.1.2); updating to 1.3 solves this issue.

Here is the backtrace:

#0  PyErr_WriteUnraisable (obj=obj@entry=<instancemethod at remote 0x7fffe7a93d20>)
    at /usr/src/debug/Python-2.7.12/Python/errors.c:664
#1  0x00007ffff7a9c078 in slot_tp_del (
    self=<FITS_rec(_uint=True, _nfields=11, _converted={}, _heapsize=0, _col_weakrefs=<WeakSet(_remove=<function at remote 0x7fffddd46de8>, _pending_removals=[], _iterating=set([]), data=set([])) at remote 0x7fffddd2f9d0>, _gap=0, _heapoffset=2881000) at remote 0x7fffddd46d70>) at /usr/src/debug/Python-2.7.12/Objects/typeobject.c:5846
#2  0x00007ffff7a96fb2 in subtype_dealloc (
    self=<FITS_rec(_uint=True, _nfields=11, _converted={}, _heapsize=0, _col_weakrefs=<WeakSet(_remove=<function at remote 0x7fffddd46de8>, _pending_removals=[], _iterating=set([]), data=set([])) at remote 0x7fffddd2f9d0>, _gap=0, _heapoffset=2881000) at remote 0x7fffddd46d70>) at /usr/src/debug/Python-2.7.12/Objects/typeobject.c:1002
#3  0x00007ffff7a7994f in insertdict_by_entry (mp=0x7fffe17e2398, key='_tiles', hash=<optimized out>, ep=<optimized out>, 
    value=<optimized out>) at /usr/src/debug/Python-2.7.12/Objects/dictobject.c:528
#4  0x00007ffff7a7b2e0 in dict_set_item_by_hash_or_entry (
    op=op@entry={'load_psf': <function at remote 0x7fffe17f60c8>, 'get_tile_radec': <function at remote 0x7fffe0d9eb90>, '_embed_sphere': None, '__package__': 'desimodel', 'yaml': <module at remote 0x7fffe17e4c90>, '_tiles': None, 'np': <module at remote 0x7fffea7cd788>, 'find_points_in_tiles': <function at remote 0x7fffe0d9ec08>, '__doc__': '\ndesimodel.io\n============\n\nI/O utility functions for files in desimodel.\n', 'load_throughput': <function at remote 0x7fffe17f6140>, 'findfile': <function at remote 0x7fffe0d9eb18>, '__warningregistry__': {('No module named specter.psf', <type at remote 0x7ffff7d83e60>, 25): True, ("Unable to import specter.throughput.load_throughput(); desimodel.io.load_throughput() won't work.", <type at remote 0x7ffff7d83e60>, 21): True, ("Unable to import specter.psf.load_psf(); desimodel.io.load_psf() won't work.", <type at remote 0x7ffff7d83e60>, 26): True, ('No module named specter.throughput', <type at remote 0x7ffff7d83e60>, 20): True}, 'warnings': <module at remote 0x7ffff7f13750>, '__bui...(truncated), key=<optimized out>, 
    hash=<optimized out>, ep=ep@entry=0x0, value=value@entry=None) at /usr/src/debug/Python-2.7.12/Objects/dictobject.c:804
#5  0x00007ffff7a7c304 in PyDict_SetItem (