Add debug output and glFlush() to gles-pbuffer-clear
Add debug output and glFlush() to gles-pbuffer-clear

This helps with showing what commands are sent to the hardware when a
given operation is executed.

Signed-off-by: Thierry Reding <b75a4d02013b0e68ae2c6bb0dcfd4b7bec282dc9@avionic-design.de>

digetx/grate,digetx/grate,grate-driver/grate,grate-driver/grate