Refactoring around checking for scipy

[bcipolli]

In refactoring imageclasses.py to distribute info into individual image classes (#323), I want to implement a simple function to check if scipy exists. I see that scipy checking is a bit varied across the code:

• Different files define their own function / decorators (imageclasses.py, tests/test_spm99analyze.py, tests/test_image_load_save.py, tests/test_image_api.py, etc), using different methods to check (ImportError, optional_package, etc)
• Some tests pass if scipy doesn't exist (even if required); other tests are skipped if scipy doesn't exist.

I suggest the following cleanup:

• Create a file utils.py, and add have_scipy() as a function.
• Use this function everywhere (in image classes where scipy status determines if they're makeable, in tests to determine if they're skippable, and other conditional logic)

Posting here just to double-check before doing the work.

[bcipolli]

Or I could just use optional_package everywhere, and ignore what's going on elsewhere... :)

[matthew-brett]

I would go for optionalpackage everywhere, and if you have the interest, refactor the other code to do the same, for consistency. I guess the older code didn't use optionalpackage because it didn't exist yet.

[bcipolli]

This was fixed in 0129ea5