Release Name: Gens 2.15.4

Notes: Gens is a Sega Megadrive, MegaCD & 32X emulator Features include:
* OpenGL support
* Joypad support
* Real Sega CD-ROM support
* Sega ISO image support
* GTK+2 integrated interface

Changes: [ 1488458 ]
opengl: optimization for ati card opengl: optimization for ati card It fixes a speed issue when using gens with some ati cards under linux. The problem is that ati driver is really bad at downloading 16 bits (RGB 5-6-5) textures; after patching, gens do buffer conversion before the downloads; I also incorporated:
- texture download now utilize glTexSubImage2D
- some gui fixes