Image constructors do not obey INHERIT

The image constructors such as DecoratedImage and Exposure do not obey the INHERIT keyword.

This is a rather murky piece of fits, but the intention of INHERIT is to allow an HDU to also read the PDU. This is necessary when reading e.g. DecoratedImage or an LSST Exposure as much of the useful information (EXPTIME etc.) is in the PDU – e.g. it's not repeated in each of the 16 amplifier HDUs.

I added support for INHERIT a while ago, but not in the code path that's used to read Images (mea culpa). For this ticket I'm going to just adjust things to call the free function that handles this correctly, but see .