Check for prereq's without `command`
- windows doesn't have this tool, but we don't really need it
Do copy the tiny_tds git repo
- the gemspec uses git ls-files
Fix cross compilation when VM host is Windows
- the default freetds sysconfdir is invalid as a folder name on windows, which you see if windows is your VM host
Don't try to check out rake-compiler-dev-box if it's already there