Correct the order of suggested syntax for extension imports
Correct the order of suggested syntax for extension imports

According to https://github.com/mitsuhiko/flask/issues/1092#issuecomment-47118613 and https://github.com/mitsuhiko/flask/pull/1085#issuecomment-45466907 , the correct order to attempt to import extensions should be flask_foo, then flask.ext.foo, then flaskext_foo.
fkazimierczak/flask,pallets/flask,mitsuhiko/flask,drewja/flask,drewja/flask,drewja/flask,mitsuhiko/flask,fkazimierczak/flask,pallets/flask,pallets/flask,fkazimierczak/flask,tristanfisher/flask,tristanfisher/flask