babel -story writes out game file with .blorb extension

[erkyrath]

If you type, for example:

./babel -story test/bronze/Bronze.zblorb

...you get the .z8 file out of the blorb, but it winds up with the filename 1810847C-0DC7-44D5-94EF-313A3E7AF257.blorb. It should be 1810847C-0DC7-44D5-94EF-313A3E7AF257.z8.

The relevant function is babel_story_story(), which calls babel_treaty(GET_STORY_FILE_EXTENSION_SEL, ...). This gets the extension for the currently loaded file, which is ".blorb", which is not what we want.

Not sure if we should update GET_STORY_FILE_EXTENSION_SEL to extract the inner game file's extension, or call something else.