Import of combined USFM broken

[postiffm]

USFM files are supposed to be separated by book. However, we added a feature to Bibledit-Desktop where you can export a combined USFM file, so that a whole Bible could be concatenated together as a single USFM. This was a help for importing the Bible into InDesign and doing auto-formatting of the Bible.

But now, if we have one of those files, the stock importer code doesn't split the USFM properly into its books.