bessel: _eval_is_real
Test is_real for besselx with real arguments
Test as_real_imag for besselx with real args
Add Tuomas Airaksinen to the AUTHORS/aboutus. Welcome to SymPy!
Delete generic BesselBase._eval_is_real and add specific ones for besselx
bessel: fix is_real tests
Merge pull request #2619 from skirpichev/tuomas2-besselj-CLEANUP

A replacement for #2566