Have function.func_globals always be dict-like

Internally we store it as either-dict-or-module, but when we expose
it to Python it needs to be given back as a mapping.  I looked briefly
into switching the internal representation, but that seemed like a much
more invasive change.

Also, add a pytest test that exposed this issue.

src/runtime/types.cpp

@@ -305,6 +305,9 @@ extern "C" BoxedFunctionBase::BoxedFunctionBase(FunctionMetadata* md, llvm::Arra
       doc(NULL) {
     assert((!globals) == (!md->source || md->source->scoping->areGlobalsFromModule()));
 
+    if (globals)
+        ASSERT(globals->cls == dict_cls || globals->cls == module_cls, "%s", globals->cls->tp_name);
+
     Py_XINCREF(closure);
     Py_XINCREF(globals);
 
@@ -1699,6 +1702,8 @@ static Box* function_globals(Box* self, void*) noexcept {
     BoxedFunction* func = static_cast<BoxedFunction*>(self);
     if (func->globals) {
         assert(!func->md->source || !func->md->source->scoping->areGlobalsFromModule());
+        if (func->globals->cls == module_cls)
+            return incref(func->globals->getAttrWrapper());
         return incref(func->globals);
     }
     assert(func->md->source);

test/integration/pytest_test.py

+import os, sys, subprocess, shutil
+sys.path.append(os.path.dirname(__file__) + "/../lib")
+
+from test_helper import create_virtenv, run_test
+
+ENV_NAME = "pytest_test_env_" + os.path.basename(sys.executable)
+ENV_DIR = os.path.abspath(ENV_NAME)
+SRC_DIR = os.path.abspath(os.path.join(ENV_NAME, "src"))
+PYTHON_EXE = os.path.abspath(os.path.join(ENV_NAME, "bin", "python"))
+
+pkg = ["pytest==2.8.2"]
+create_virtenv(ENV_NAME, pkg)
+PYTEST_DIR = os.path.abspath(os.path.join(SRC_DIR, "pytest"))
+
+test_dir = os.path.join(ENV_DIR, "tests")
+if not os.path.exists(test_dir):
+    os.mkdir(test_dir)
+
+with open(os.path.join(test_dir, "test_foo.py"), 'w') as f:
+    f.write("""
+import pytest
+@pytest.mark.skipif(True, reason="for fun")
+def test_skipif_true():
+    1/0
+""")
+
+subprocess.check_call([os.path.join(ENV_DIR, "bin", "py.test"), test_dir])
+# subprocess.check_call(["gdb", "--args", PYTHON_EXE, "-m", "pytest", test_dir])
+
+

test/tests/functions.py

@@ -97,3 +97,19 @@ g2 = copyfunc(g)
 assert g.func_defaults == g2.func_defaults, (g.func_defaults, g2.func_defaults)
 g(1)
 g2(2)
+
+
+# Regression test: make sure that __globals__/func_globals gets set
+# properly in exec cases
+d = {}
+exec """
+def f():
+    pass
+""" in d
+assert type(d['f'].__globals__) == dict
+
+exec """
+def f():
+    pass
+""" in globals()
+assert type(globals()['f'].__globals__) == type(globals())