Various fixes for issues found during testing.
More sanity checks added to the library.
Previously CTA (SPS Disk Image Analyser) did not attempt to mimic the real disk when an IPF was loaded, due to various limitations in the library. Since these limitations no longer apply, CTA‘s behaviour has been changed to fully simulate a dump file when loading an IPF, useful for example when examining a real dump vs. an IPF file. Now, apart from the perfect density graph nothing much (should) differ between a real dump used to generate an IPF and the IPF generated from the same game.