Metadata->Add format file dialog does not include .cbc format as acceptable

[Kirtai]

When adding a new format to a book using the "Add a new format" on the "Edit Meta Information" window, the file dialog defaults to a filter called Books which does not include *.cbc even though this is a valid book type.

The fix would simply to be to add *.cbc to the Books filter

[kovidgoyal]

Fixed in branch trunk. The fix will be in the next release.