A couple unit tests are infinite-looping when running against scala 2.13

[erikerlandson]

I disabled these in #759, with comments.

[gabrieljones]

spire/tests/src/test/scala/spire/math/ComplexCheck.scala

Lines 74 to 78 in 6d2409b

	if (spire.scalacompat.preScala2p13) {
	// this test inf-loops on scala 2.13
	implicit val threshold = BigDecimal(1e-14) // 532788694 + 329i has log-error-ratio 1.1e-15
	logNear(x.nroot(2).pow(2), x)
	}

Found this one. Where are the others?

[gabrieljones]

spire/tests/src/test/scala/spire/math/AlgebraicTest.scala

Lines 273 to 287 in 6d2409b

	if (spire.scalacompat.preScala2p13) {
	Gen.oneOf(
	genRational.map { q => RationalAlgebraic(Algebraic(q), q) },
	genBigDecimal,
	genDouble,
	genLong
	)
	} else {
	// Scala 2.13 has bugs around the construction of BigDecimal quantities
	Gen.oneOf(
	genRational.map { q => RationalAlgebraic(Algebraic(q), q) },
	genDouble,
	genLong
	)
	}

Found a second reference to spire.scalacompat.preScala2p13

[kschwarz1116]

Attempted to address since the issue linked from the PR is fixed, however I seem to be running into a similar issue with scala 3 instead. I wonder if that change never made it into dotty. I'll keep digging.