renderercommon: removed libjpeg version hard check
cgame: fixed accuracy and hs ratio in console output, refs #478
renderercommon: readded JPEG version check with libjpeg-turbo v6 API/ABI support

Unlike many other distributions, Fedora ships libjpeg-turbo with libjpeg v6 API/ABI full compatibility.
client: removed COM_StripExtension3 in renderer2