Fix Issue 7006 - std.math.pow (integral, integral) crashes on negative exponents

[ghost]

I improved the docs too, including the public unittest.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	7006	regression	std.math.pow (integral, integral) crashes on negative exponents

⚠️⚠️⚠️ Warnings ⚠️⚠️⚠️

• Regression or critical bug fixes should always target the stable branch. Learn more about rebasing to stable or the D release process.

To target stable perform these two steps:

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + phobos#7322"

[thewilsonator]

Otherwise looks good.

[ghost]

I do not understand, why this always fails on ci/circleci. First I thought it is unrelated, but meanwhile the error was reproduced with each run: std/range/package.test fails. When I run that test locally it succeeds (but needs about 6 minutes). What does ci/circleci actually do?

[thewilsonator]

Circle is green now, but mir/algorithm still fails consistently.

[ghost]

Circle is green now, but mir/algorithm still fails consistently.

Found (and fixed) the problem: m <= -1 is not a good idea, when m is unsigned. I added also a unittest (assert(pow(0,uint.max) == 0);) to guard for that problem. (There are two more expressions I put into static if, but that is mere for extra security; IMHO they could not break and therefore I could not add a guarding unittest for them.)