NOTE: when using Evas_Object image preload infrastructure the GL texture
upload was uploaded from the main loop during the rendering stage. This
could lead to some frame drop during fast animation due to the time needed
to upload that texture.
This patch fix this problem by uploading a small texture quickly (16x16)
and waiting for going back to the main loop to be able to use the same GL
context from another thread to do the texture upload asynchronously without
blocking the main loop.
Evas_Common.h should be used for the public header, and rather rename
evas_common.h internal header to another name.
Sa:
Evas_Common_Header.h -> Evas_Common.h
evas_common.h -> evas_common_private.h
Shouldn't have both Evas_Common.h and evas_common.h because of case
insensitive filesystems.