Automate Windows builds #77

The process for creating Windows builds is manual and error-prone. There should be a bash script (run under MSYS) or batch file that:

1. Fetches a particular commit from the git or svn repository
2. runs make clean, then makes bitcoin.exe and bitcoind.exe
3. copies or exports all of the source files into the setup/src folder
4. copies bitcoin.exe to setup/ and bitcoind.exe to setup/daemon
5. runs command-line 7za.exe to create the setup .zip file
6. runs command-line nsis installer to create the setup .exe file

Done, currently done via gitian on the 0.3.22 rc/s releases.