BUG: signal: Use np.linspace instead of np.arange to fix an off-by-one error that could occur in dstep and dimpulse.
Merge pull request #2663 from WarrenWeckesser/bug-dstep-dimpulse

BUG: signal: Use np.linspace instead of np.arange to fix an off-by-one error that could occur in dstep and dimpulse.