Add a check on iterations when Halley iterating.

Correct igamma inverse initial calculations, and adjust digits needed for convergence.
Fix erf calculation limits.
Adjust non-convergence behaviour in Halley iteration.
For issue #3408.

[SVN r56598]

libs/math

@@ -1 +1 @@
-Subproject commit 71940bec79ba9ad712d1481f23e4f1cb134d327f
+Subproject commit 2e07572fafa6313dbfd2563b86eb1dcea7043ab8