Add test case for global stmt at module level.

Fix test_grammar so that it ignores warning about global stmt at
module level in exec.

Lib/test/output/test_global

@@ -2,3 +2,4 @@ test_global
 got SyntaxError as expected
 got SyntaxError as expected
 got SyntaxError as expected
+got SyntaxError as expected

Lib/test/test_global.py

@@ -37,3 +37,9 @@ def wrong3():
     global x
 """
 compile_and_catch_warning(prog_text_3)
+
+prog_text_4 = """
+global x
+x = 2
+"""
+compile_and_catch_warning(prog_text_4)

Lib/test/test_grammar.py

@@ -411,6 +411,9 @@ if g.has_key('__builtins__'): del g['__builtins__']
 if g != {'z': 1}: raise TestFailed, 'exec \'z = 1\' in g'
 g = {}
 l = {}
+
+import warnings
+warnings.filterwarnings("ignore", "global statement", module="<string>")
 exec 'global a; a = 1; b = 2' in g, l
 if g.has_key('__builtins__'): del g['__builtins__']
 if l.has_key('__builtins__'): del l['__builtins__']