Draw only the skybox.
Updated the default cubemap to be more Pioneer-esque.
SDL_GL_SetAttribute is supposed to be called *before* creating the window

The previous code was just weird and broken.

This fixes progress bars, which need the GL draw buffer to have an alpha
channel (previously they worked for some people, depending on what buffer
layout SDL happened to pick).
Fix the default constructor!
auto-commit: translation updates
Merge remote-tracking branch 'johnbartholomew/fix-progress-bars'
Merge branch 'gl-matrix-optimisations'
silence signed comparison warning
box test with variable and fixed elements
Moved the SectorCache out of SectorView so it can be used elsewhere like LuaStarSystem.
Initial rewrite of Box layout

A Box needs to be constrained to the area given to it by its parent
container. Letting it position elements off-screen is not useful as well
as making it impossible to embed a Box in a container that can provide
it with more space (eg Scroller).
define YIELD for mingw
Merge branch 'master' of github.com:fluffyfreak/pioneer into skybox

Conflicts:
	src/Background.cpp
force the player face to expand into the space
Merge remote-tracking branch 'anttisalonen/master'
extra build support for clang+ccache
auto-commit: translation updates
Merge branch 'master' of https://github.com/pioneerspacesim/pioneer into Shields
Corrected a comment stating what the file/class is actually for.
Use the sector cache everywhere possible.
Enable and disable the star for hyperspace.