catch missing extras instead of deferring to setuptools

[DropD]

at load, check if there are extras, if yes:

try:
import_module
except ImportError:
print 'maybe missing extras?'

[ltalirz]

@DropD Is this still relevant?

If yes, could you perhaps describe the issue in a bit more detail so that it can be fixed by someone else?
Part of the description on "extras" (which extras are you referring to here?) could go in the README under the "What for" section.

I've had a look at the "What for" section and it is not clear to me whether it is still accurate or not.
In essence, it says reentry is fast because it ignores extra dependencies. But isn't the main speed advantage the cache?

[ltalirz]

@DropD By the way, the entry-point specification now says

Using extras for an entry point is no longer recommended. Consumers should support parsing them from existing distributions, but may then ignore them. New publishing tools need not support specifying extras. The functionality of handling extras was tied to setuptools’ model of managing ‘egg’ packages, but newer tools such as pip and virtualenv use a different model.

I.e. we might simplify our life by removing corresponding code.

Does this mean that reentry is obsolete? If not, we definitely need to adjust the "What for" section of the reentry README