We have a number of checks to see if we can import certain modules. For

these, we use a combination of import statements and imp.find_module

calls. The reason is that some modules would fail to import on some

systems using imp.find_module.
The reason for that is that imp.find_module doesn't use registered

importers, and therefore can't find modules in zipped eggs. Furthermore,

our usage would cause leaked open file handles, since if the module is

represented by a .pyc file, imp.find_module would pre-import it.
Instead of dealing with all this, I've added a new, single function for

checking if modules can be imported. All checks in the codebase now use

this instead, giving us consistency and fixing the issues with zipped

eggs.

Unit tests pass.
The dev server could be run against Pillow, which wasn't working here before.
Hand-tested some of our modules that are more complex (like the S3 support in

django-storages), with and without the module.