BUG: correlate was extremely slow when in2.size > in1.size
STY: PEP8 fixes for signaltools test (partially autopep8)
TST: Add a test for swapping of inputs
when in2 is bigger than in1, test reversal in 3 dimensions and complex conjugation
WHT: signal: more pep8 in tests
Merge pull request #3664 from pr-3664

BUG: signal: correlate was extremely slow when in2.size > in1.size

This change swaps the inputs if the first is smaller, but then reverses
and conjugates the output to undo the effects of the reversal.