Improved error messages and added tentative fixes for HP Tru64: the compiler appears to store constants that should underflow to zero as a small non-zero values which messes up the logic used in the test cases.

[SVN r40963]

libs/math

@@ -1 +1 @@
-Subproject commit 40b2cc09677fac977d6a57dfe9bf2f2b13e34a01
+Subproject commit bf1404a2dfd793917446956c1fcf94cfe2134b7f