tests/basic/: Make various tests skippable.

To run the testsuite on small ports.

tests/basics/op_error_memoryview.py

@@ -0,0 +1,19 @@
+# test errors from bad operations (unary, binary, etc)
+try:
+    memoryview
+except:
+    import sys
+    print("SKIP")
+    sys.exit()
+
+def test_exc(code, exc):
+    try:
+        exec(code)
+        print("no exception")
+    except exc:
+        print("right exception")
+    except:
+        print("wrong exception")
+
+# unsupported binary operators
+test_exc("m = memoryview(bytearray())\nm += bytearray()", TypeError)