COMMON: Automatically handle RISC OS files with NFS extensions

[ccawley2011]

RISC OS typically uses a 3 digit hexadecimal value in the file system metadata instead of file extensions. Since this is difficult to preserve on non-RISC OS systems, many emulators and file sharing tools append it to the file name after a comma.

Since the extension may or may not be present depending on how the user dumped the files, it would be useful for ScummVM to be able to transparently handle these extensions when present.

This currently affects the AGOS and Freescape engines, and is likely to affect other engines in the future.

[neuromancer]

The freescape engine is not currently reading any RISC OS files, so it shouldn't be affected?

[ccawley2011]

Not yet - I'd assumed it already had the basics for 3D Construction Kit in place. It will be affected once that's supported.