Support stacktrace on Windows

Must be built with `CONFIG += strace_win`

Code is taken from [Quassel IRC project (GPL v2/3)](https://gitorious.org/quassel/quassel/blobs/0.8/src/common/logbacktrace_win.cpp) and [slightly modified](https://gist.github.com/892412d9818c8f30dde0)

On crash a dialog box with product and libraries versions and the actual backtrace will be shown
http://img4.imageshack.us/img4/1487/strace.png

It is highly recommended to ship pdb file (debug info generated) with application, otherwise function name unmangling will not be possible