tests: Rename test scripts, changing - to _ for consistency.

From now on, all new tests must use underscore.

Addresses issue #727.

tests/basics/fun_defargs.py

@@ -0,0 +1,20 @@
+def fun1(val=5):
+    print(val)
+
+fun1()
+fun1(10)
+
+def fun2(p1, p2=100, p3="foo"):
+    print(p1, p2, p3)
+
+fun2(1)
+fun2(1, None)
+fun2(0, "bar", 200)
+try:
+    fun2()
+except TypeError:
+    print("TypeError")
+try:
+    fun2(1, 2, 3, 4)
+except TypeError:
+    print("TypeError")