Bring back debug MSVC builds for underlying libs. Mixing runtimes doesn't work well with MSVC.
libtorent build cleanup
qBt Qt4 msvc fixes
Support qBt MinGW builds
Add debug helper library to msvc build
Mingw release deployment fixups
Update iss script to support mingw and msvc versions
qBt master has changed version strings, adopt accordingly. We need to enable delayed variable expansion in batch files to get correct version string.