(-1)**n is integer for integer n
abs((-1)**n) = 1 for integer n
Evaluate sin(pi*n/2) for integer n
Evaluate cos(pi*n/2) for integer n
Implement Add.is_rational method
(-1)**n is odd for integer n
Implement AskEvenHandler.Pow method
Evaluate (-1)**((-1)**n/2 -/+ S.Half) as (-1)**n or (-1)**(n + 1)
UnXFAIL Wester test_I3 and test_I4
Revert "Evaluate (-1)**((-1)**n/2 -/+ S.Half) as (-1)**n or (-1)**(n + 1)"

This reverts commit fdb8e3ed6b0dd5d9c5855a1021ca7a8a680351cb.
Refine (-1)**((-1)**n/2 -/+ S.Half) as (-1)**n or (-1)**(n + 1)
Adopt Wester test_I4 (use refine)
Merge pull request #2316 from skirpichev/unxfail-wester-I3-I4

UnXFAIL Wester tests I3, I4