ignore files in github
add 4.5.1 url to NSIS component
Fix for detection of 4.5.1 on Windows 8.1

as per Aaron Stebner's blog post
http://blogs.msdn.com/b/astebner/archive/2013/11/11/10466402.aspx
Merge pull request #5 from bveenvliet/master

Fix 4.5.1 detection problem on Windows 8.1