psFitsAlloc() needs a second mode argument (r/w/a)

[rhl@…]

The current definition of psFItsAlloc doesn't specify if the file should be opened for read or write.
Additionally, if the file can be opened for append, we have a way to create multi-extension FITS
files when desireable.

If a non-existent file is opened for read the psFitsAlloc() call doesn't fail, but instead creates
a 2880-byte file; a later attempt to psFitsReadImage() the file fails as the file contains no
data (but we shouldn't get that far)

I propose that the prototype be changed to:

psFits *psFitsAlloc(const char *name, const char *mode);

where mode can be "r", "w", or "a" (by analogy to fopen)

The function should return NULL if it is unable to open the file in the desired mode.

[eugene]

this has been added to the SDRS (v.15)

[Paul Price]

Now called psFitsOpen.