Wait until images are loaded

When building ABP for Safari on my local machine or the build server, the result of Image.open was always none. It appears [1] that Image.open is lazy, and we need to call .load() to ensure that the image is actually loaded.

Note that this is already pushed:
https://hg.adblockplus.org/buildtools/rev/60153820143b

[1] http://stackoverflow.com/a/12413650

[Sebastian Noack, 2013-11-16 14:48:40]

Normally this isn't necessary. But some distros come with a broken or old
version of PIL, which requires that hack, in some cases.

However you should also add it after Image.open() in filter_blend(). And please
add a comment, since this is a hack which is only required in some environments.

[Felix Dahlke, 2013-11-16 15:13:45]

Alright, here's a new patch.

[Sebastian Noack, 2013-11-16 15:19:56]

LGTM. Please remember to update .hgsubstate in sitescripts and
adblockpluschrome. You forgot it, when you pushed the initial version of that
fix.

[Wladimir Palant, 2013-11-17 06:11:40]

LGTM