cogl: Declare cogl_is_bitmap()
cogl: Declare cogl_is_bitmap()

The function is automatically defined by the CoglHandle type
definition macro, but it still requires to be declared in the
header file to be used.

spatulasnout/cogl,Distrotech/cogl,Distrotech/cogl,collects/cogl,djdeath/cogl,gcampax/cogl,djdeath/cogl,gcampax/cogl,Distrotech/cogl,spatulasnout/cogl,djdeath/cogl-android,djdeath/cogl-android,gcampax/cogl,djdeath/cogl,collects/cogl,djdeath/cogl-android,gcampax/cogl,Distrotech/cogl