fix "r_ignorehwgamma 1" and add support for "r_ignorehwgamma -1".
r_ignorehwgamma meaning:
-1	force hardware gamma.
 0	auto detect.
 1	force software gamma.

---
 code/sdl/sdl_gamma.c |    2 +-
 code/sdl/sdl_glimp.c |    6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

Index: quake3/code/sdl/sdl_gamma.c
===================================================================
--- quake3.orig/code/sdl/sdl_gamma.c
+++ quake3/code/sdl/sdl_gamma.c
@@ -39,7 +39,7 @@ void GLimp_SetGamma( unsigned char red[2
 	Uint16 table[3][256];
 	int i, j;
 
-	if( !glConfig.deviceSupportsGamma || r_ignorehwgamma->integer )
+	if( !glConfig.deviceSupportsGamma || r_ignorehwgamma->integer > 0 )
 		return;
 
 	for (i = 0; i < 256; i++)
Index: quake3/code/sdl/sdl_glimp.c
===================================================================
--- quake3.orig/code/sdl/sdl_glimp.c
+++ quake3/code/sdl/sdl_glimp.c
@@ -733,6 +733,12 @@ success:
 	// http://bugzilla.icculus.org/show_bug.cgi?id=4316
 	glConfig.deviceSupportsGamma = SDL_SetGamma( 1.0f, 1.0f, 1.0f ) >= 0;
 
+	if ( -1 == r_ignorehwgamma->integer)
+		glConfig.deviceSupportsGamma = 1;
+
+	if ( 1 == r_ignorehwgamma->integer)
+		glConfig.deviceSupportsGamma = 0;
+
 	// get our config strings
 	Q_strncpyz( glConfig.vendor_string, (char *) qglGetString (GL_VENDOR), sizeof( glConfig.vendor_string ) );
 	Q_strncpyz( glConfig.renderer_string, (char *) qglGetString (GL_RENDERER), sizeof( glConfig.renderer_string ) );