openbor Tools

Fixed some PC joystick bugs:
* Fixed control configuration when the interface is being controlled by a joystick. Reported by magggas.
* Fix the detection of PlayStation, Xbox, and GP2X controllers. OpenBOR was misdetecting my Microsoft SideWinder Freestyle Pro as an Xbox controller just because it had "Microsoft" in its name.

Actually fixed the palette bug that I tried to work around in r2917.

Added fixed-function gamma correction and entirely removed all GLSL code. Now even users with fixed-function GPUs can have completely accelerated brightness/gamma correction, including fading!

OpenGL: implemented gamma correction using the fixed-function pipeline. OpenGL 1.3 (from 2001) is now the minimum version, but older cards with no GLSL support can now use GPU-accelerated brightness and gamma correction."

Several interconnected changes:
* define OPENGL, LOADGL, and TREMOR macros in the makefile
* use the above macros in the code, making it easier to read, maintain, and port
* some general cleanup of makefile
* enable GPU-accelerated brightness/gamma correction in OpenGL
* OpenGL: do brightness correction with the fixed-function pipeline; this is a better way to do it even for GPUs that support GLSL. However, GLSL is still used for both brightness and gamma when gamma correction is requested.
* OpenGL: remove dead/disabled code
* dynamically load OpenGL libraries on OS X

Fixed tracerealloc() on Windows by implementing a pseudo-realloc() function instead of relying on the buggy realloc() implementation in the Windows CRT.

loadgl: load glGetError and glUniform4f

Fixed previews in the SDL mod selection menu for mods using data/bgs/title.png instead of data/bgs/title.gif.

Added a clearscreen() builtin function to the script API. It takes a screen pointer as input, and clears the entire screen to solid black.
The clearscreen() script function is a simple wrapper around the clearscreen() function in gamelib.

Usage: void clearscreen(void* screen)

Note: this has not been tested yet.

Reverted most of r2865. It introduced several issues and large chunks of new but unmaintained code. A few fixes and improvements that could have stayed are reverted as part of this, but they can be re-added later if necessary.