Install also test libs on Windows.

Resolves DLL hell when running tests.
Fix linker errors with Framebuffer::BufferAttachment::* on Windows.
Text: don't use std::u32string on MinGW.

MinGW (or Windows at general?!) somehow doesn't expect four-byte
characters in a string and this class fails miserably when freeing
memory. Replaced with std::vector<char32_t>, it's horrendously ugly
solution, but I hope this will be resolved soon with newer MinGW GCC
(4.7.2 fails).