integer tests are likely to miss zero

The integer tests use genrand_int32 to fill the input buffers used by the tests. This is generally not a problem, except that for the larger scalar types, int and long, the probability that the relatively few samples that are tested contain zero is low. This is particularly unfortunate for functions such as popcount(), clz(), and ctz() where getting the correct result for a zero input is especially important. We should have a way to ensure that 0 and other interesting values are guaranteed to be tested.

Start by locating the integer tests that use genrand_int32 to fill input buffers. Ensure zero and other interesting values are guaranteed in the samples, then verify that cases such as popcount(), clz(), and ctz() exercise zero inputs correctly.

Written by the indexing model from the issue text.