g_format_size() is broken on Windows

Submitted by Allison (desrt)

Description

g_format_size() attempts to use the ' printf modifier to format the full byte size with separators (ie: the "123,456,789 bytes" part).

This doesn't exist on Windows, and it appears that our built-in printf deals with it by passing it straight through.

For now, I'll disable the use of ' on Windows (so we will just see "123456789 bytes") but it is clear that we should attempt to find a better solution.