These routines allow default directories and file extensions to be set and used
by the FITS Io and region pool routines.
Valid values for the DEFDIRENUM argument can be found in
shCFitsIo.h.
This routine will set the default directory and or default extension for reading
from a file into a region or from the pool.
This routine will return a pointer to the default directory and extension for
reading into a region from a file or from the pool. Storage for 'a_dir' and
'a_ext' must be allocated in the calling routine. This storage must be
sufficient to hold the directory and file extension.
shDirSet
shDirGet