tests/float: Add tests for math funcs that return ints.

One should test bigint, inf and nan to make sure all cases are covered.

tests/float/math_fun_int.py

+# test the math functions that return ints
+
+try:
+    import math
+except ImportError:
+    print("SKIP")
+    import sys
+    sys.exit()
+
+for fun in (math.ceil, math.floor, math.trunc):
+    for x in (-1.6, -0.2, 0, 0.6, 1.4, float('inf'), float('nan')):
+        try:
+            print(fun(x))
+        except (ValueError, OverflowError) as e:
+            print(type(e))

tests/float/math_fun_intbig.py

+# test the math functions that return ints, with very large results
+
+try:
+    import math
+except ImportError:
+    print("SKIP")
+    import sys
+    sys.exit()
+
+for fun in (math.ceil, math.floor, math.trunc):
+    for x in (-1e25, 1e25):
+        print('%.3g' % fun(x))