GRIM/EMI: Fix compile warnings
GRIM/EMI: Use proper GL constants
TINYGL: Fix coverity and compile warning

- change void* to byte*, otherwise delete[] is undefined
GRIM/EMI: Fix compile warning

- the pixel data retrieved via getPixels() is stored as non-const
data in pixebuffer, so the original object can't be const
Merge pull request #833 from chkr-private/compiler-warning-fixes

EMI/GRIM/TINYGL: fix compile warnings and coverity issues