fix wxQt compilation
backing out previous change; should be fixed in wxQt
Upgrade MSVS solution and projects to MSVS 2012 version.

Also don't use the version number in the solution file name, it is not used in
the projects anyhow.
Change build directories in MSVS projects.

Create everything under $(Platform)\$(Configuration) to make it easier to
delete all build files and also to ensure that versit.dll ends up near M.exe
to allow running it without explicitly copying it anywhere.
Update MSVS solution file to MSVS 2013 version.

No real changes, the solution and projects are compatible with 2012.
Change default disposition to "attachment" for the text parts.

This is more useful by default.