Add support for cross compiling a multi platform (x64-mingw32 and x86-mingw32) fat binary gem and support for native builds on Windows.

This moves all MiniPortile recipes into extconf.rb. This enables
native build on Windows and ensures that all depending libraries
are build with the same compiler version as the C-ext when cross compiling.
Use 'host' as alternative, because host_alias is not set on RubyInstaller-1.9.3
Remove libxslt patches that modify configure.in.

Modifications to configure.in trigger a re-run of autotools,
which adds additional dependencies to nokogiri. This breaks the build
of libxslt when there is a version mismatch between the one used to
release the libxslt tar file and the installed one.

The removed patches itself are IMHO not necessary for nokogiri.
Add missing files to Manifest.txt
Update rake-compiler version to 0.9.2 in order to avoid 'win32/resolv' error.
Move gem post install message into cross compiling callback, so that it
is really used for the packaged fat binary gems.

Avoid adding dependency.yml twice - once per Manifest.txt and once
per add_file_to_gem.
Don't trigger gem task twice in 'rake gem:windows'.

It was called as prerequisites and is called as part of
'rake cross native gem'
Use a better fix for the character escaping bug in MSYS
Merge branch 'mingw32-support' of https://github.com/larskanis/nokogiri into larskanis-mingw32-support