Added Image Manager 1024 emulation. Patch from John Elliott.

src/ibm.h

@@ -516,6 +516,8 @@ enum
         GFX_OTI037,     /*Oak OTI-037*/
         GFX_COMPAQ_CGA,	/*Compaq CGA*/
 	GFX_SIGMA400,	/*Sigma Designs Color 400 */
+	GFX_PGC,	/*Professional Graphics Controller */
+	GFX_IM1024,	/*Vermont Microsystems IM1024 */
         GFX_MAX
 };