make loaders use "big image" macro to detect an image that is going to just

make loaders use "big image" macro to detect an image that is going to just
be way too big to ever allocate. probably code can do with other fixes too.

also make jpeg loader rudametarily understand load regions. very brute-force.
but enough for just this moment to do testing.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/evas@42507 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33