BUG: in integrate/quadpack.h, put all declarations before statements.

This was causing a build failure on some Python 3.4 systems due to
-Werror=declaration-after-statement being used there by accident
(see http://bugs.python.org/issue21121)

Issue was introduced in gh-2362.
Merge pull request #3774 from rgommers/decl-after-statement

BUG: in integrate/quadpack.h, put all declarations before statements.