Fix mingw64 gcc 4.9 compiler warnings.

fixes this warning from gcc.

warning: #warning Please include winsock2.h before windows.h
Initial import of mpir-2.6.0. According to www.mpir.org mpir-2.6.0 can be used as a drop-in replacement for gmp as it is a fork of it. More importantly mpir has excellent supportfor MS Visual Studio toolset. This will help with porting mlton to native windows without mingw/cygwin.
upgraded solution to Visual studio 2012.
updated test project files to VS2012.
updated try projects.
added .gitignore file for the whole of mpir-2.6.0 project.
Updated .gitignore file to ignore runtime build generated hello.s file
updated .gitignore file
Merged changes from branch 'mingw64_build_2'