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

From now on, all new tests must use underscore.

Addresses issue #727.

tests/basics/generator_closure.py

@@ -0,0 +1,26 @@
+# a generator that closes over outer variables
+def f():
+    x = 1 # closed over by g
+    def g():
+        yield x
+        yield x + 1
+    return g()
+for i in f():
+    print(i)
+
+# a generator that has its variables closed over
+def f():
+    x = 1 # closed over by g
+    def g():
+        return x + 1
+    yield g()
+    x = 2
+    yield g()
+for i in f():
+    print(i)
+
+# using comprehensions, the inner generator closes over y
+generator_of_generators = (((x, y) for x in range(2)) for y in range(3))
+for i in generator_of_generators:
+    for j in i:
+        print(j)