vwebp: work around the transparent background with GLUT bug
vwebp: work around the transparent background with GLUT bug

we setenv XLIB_SKIP_ARGB_VISUALS=1 before any GLUT call.

Change-Id: I4cff5b6c6155d5a074fa22fe56219f241558666e

ttyangf/libwebp,PKRoma/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,ttyangf/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,ttyangf/libwebp,webmproject/libwebp,ttyangf/libwebp,ttyangf/libwebp,webmproject/libwebp,PKRoma/libwebp