Updated the sign functions to use Johan Rade's fp-utilities code.

Added tests for the sign functions.
Added docs for the sign functions and moved some sections around.

[SVN r51793]

libs/math

@@ -1 +1 @@
-Subproject commit e38209bdc083eed10fff4a4e640717b0aa07994b
+Subproject commit a935d5e1cd0f286f703d38ded96d74c0362a25fb