Inconsistent file extension handling

[hcs64]

The input setup will try set the input file extensions to .subcode and .toc, with the intention that it can be used with just image_name and it will find image_name.subcode and image_name.toc. But if the image name has a dot in it like image.name, then the final part gets replaced (image.subcode).

Better logic would be:

• Try opening as-is (so it can be called, as in previous versions, with image_name.subcode)
• If not found, try adding (not replacing) .subcode

Then to find the toc:

• If the subcode was successfully opened in a file ending in .subcode, replace the extension with .toc
• Otherwise probably just don't try to find the toc? Maybe try adding it?
• Take a command line option that specifically says where to find the toc?