bpo-29706: Test that IDLE colors async/await as keywords. (GH-6846)

Added to the eye-verified htest, not to the unittests.
Also remove some stray leftover comments.
(cherry picked from commit 389a48ed)
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Lib/idlelib/colorizer.py

@@ -17,8 +17,6 @@ def make_pat():
     builtinlist = [str(name) for name in dir(builtins)
                                         if not name.startswith('_') and \
                                         name not in keyword.kwlist]
-    # self.file = open("file") :
-    # 1st 'file' colorized normal, 2nd as builtin, 3rd as string
     builtin = r"([^.'\"\\#]\b|^)" + any("BUILTIN", builtinlist) + r"\b"
     comment = any("COMMENT", [r"#[^\n]*"])
     stringprefix = r"(?i:r|u|f|fr|rf|b|br|rb)?"
@@ -268,13 +266,14 @@ def _color_delegator(parent):  # htest #
         "else: float(None)\n"
         "if iF + If + IF: 'keyword matching must respect case'\n"
         "if'': x or''  # valid string-keyword no-space combinations\n"
+        "async def f(): await g()\n"
         "# All valid prefixes for unicode and byte strings should be colored.\n"
         "'x', '''x''', \"x\", \"\"\"x\"\"\"\n"
         "r'x', u'x', R'x', U'x', f'x', F'x'\n"
         "fr'x', Fr'x', fR'x', FR'x', rf'x', rF'x', Rf'x', RF'x'\n"
         "b'x',B'x', br'x',Br'x',bR'x',BR'x', rb'x'.rB'x',Rb'x',RB'x'\n"
         "# Invalid combinations of legal characters should be half colored.\n"
-        "ur'x', ru'x', uf'x', fu'x', UR'x', ufr'x', rfu'x', xf'x', fx'x'"
+        "ur'x', ru'x', uf'x', fu'x', UR'x', ufr'x', rfu'x', xf'x', fx'x'\n"
         )
     text = Text(top, background="white")
     text.pack(expand=1, fill="both")