Added native NSIS compression and corrected EstimatedSize in registry

For more information on this pull request see:

https://github.com/JuliaLang/julia/commit/0b46af57322aa491d59f6c8e4b334e506cd64889

Adding native LZMA should give you better compression and a quicker installer start and save you some Makefile lines. The bad part of it is that the build takes a little longer to finish when executing "make dist".

Also fixed a small bug related to the "Uninstall or change a program dialogue" in the Control Panel which declared the size of the Julia distribution to be 300 KB.