tests: Add "with" statement testcases.

tests/basics/with-break.py

+class CtxMgr:
+
+    def __enter__(self):
+        print("__enter__")
+        return self
+
+    def __exit__(self, a, b, c):
+        print("__exit__", repr(a), repr(b))
+
+for i in range(5):
+    print(i)
+    with CtxMgr():
+        if i == 3:
+            break

tests/basics/with-continue.py

+class CtxMgr:
+
+    def __enter__(self):
+        print("__enter__")
+        return self
+
+    def __exit__(self, a, b, c):
+        print("__exit__", repr(a), repr(b))
+
+for i in range(5):
+    print(i)
+    with CtxMgr():
+        if i == 3:
+            continue

tests/basics/with-return.py

+class CtxMgr:
+
+    def __enter__(self):
+        print("__enter__")
+        return self
+
+    def __exit__(self, a, b, c):
+        print("__exit__", repr(a), repr(b))
+
+def foo():
+    with CtxMgr():
+        return 4
+
+print(foo())

tests/basics/with1.py

+class CtxMgr:
+
+    def __enter__(self):
+        print("__enter__")
+        return self
+
+    def __exit__(self, a, b, c):
+        print("__exit__", repr(a), repr(b))
+
+
+with CtxMgr() as a:
+    print(isinstance(a, CtxMgr))
+
+try:
+    with CtxMgr() as a:
+        raise ValueError
+except ValueError:
+    print("ValueError")
+
+
+class CtxMgr2:
+
+    def __enter__(self):
+        print("__enter__")
+        return self
+
+    def __exit__(self, a, b, c):
+        print("__exit__", repr(a), repr(b))
+        return True
+
+try:
+    with CtxMgr2() as a:
+        raise ValueError
+    print("No ValueError2")
+except ValueError:
+    print("ValueError2")
+
+
+# These recursive try-finally tests are attempt to get some interpretation
+# of last phrase in http://docs.python.org/3.4/library/dis.html#opcode-WITH_CLEANUP
+# "If the stack represents an exception, and the function call returns a ‘true’
+# value, this information is “zapped” and replaced with a single WHY_SILENCED
+# to prevent END_FINALLY from re-raising the exception. (But non-local gotos
+# will still be resumed.)"
+print("===")
+with CtxMgr2() as a:
+    try:
+        try:
+            raise ValueError
+            print("No ValueError3")
+        finally:
+            print("finally1")
+    finally:
+        print("finally2")
+
+print("===")
+try:
+    try:
+        with CtxMgr2() as a:
+            try:
+                try:
+                    raise ValueError
+                    print("No ValueError3")
+                finally:
+                    print("finally1")
+            finally:
+                print("finally2")
+    finally:
+        print("finally3")
+finally:
+    print("finally4")