demos: c_simple: blittest: Correct caption.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
build: check_symbols: Add loaders.

Loaders are separate library now, add symbol checks for them too.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
demos: c_simple: blittest: Add check.

Add check if sprite was sucesfully loaded.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>