Add prototypes to get the mathmodule.c to compile on OSF1 5.1 (Tru64)
and eliminate a compiler warning in floatobject.c.  There might be
a better way to go about this, but it should be good enough for now.
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 5e52e78..0440871 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -12,6 +12,11 @@
 #endif /* __STDC__ */
 #endif /* _MSC_VER */
 
+#ifdef _OSF_SOURCE
+/* OSF1 5.1 doesn't make this available with XOPEN_SOURCE_EXTENDED defined */
+extern double copysign(double, double);
+#endif
+
 /* Call is_error when errno != 0, and where x is the result libm
  * returned.  is_error will usually set up an exception and return
  * true (1), but may return false (0) without setting up an exception.