fix invalid casts and index overflows in signal.Pool

(ws/stride/pad may be int32 or int64; int32*->int64* is a strict aliasing violation, int64->int32 is a possible overflow) https://bugs.debian.org/878596

fix invalid casts and index overflows in signal.Pool
dce26933 · Rebecca N. Palmer · 5561f5d6 · dce26933
--- a/theano/tensor/signal/pool.py
+++ b/theano/tensor/signal/pool.py