For the time being, development is done in both the Windows
(IStream/IStorage) and portable (libgsf) versions.  This is because the
test coverage is slightly worse in the libgsf version---some tests fail
only in that version.

The pre-gsf branch is developed with the mingw cross-compiler and wine.
The master branch, which uses libgsf, is developed both with mingw+wine
(though some tests fail) and native tools.