don't convert (unindexed) ascii str to bytes in GenericProperty#100

pnico wants to merge 3 commits intoGoogleCloudPlatform:mainGoogleCloudPlatform/appengine-python-standard:mainfrom

freshplanet:fix/generic-property-ascii-strfreshplanet/appengine-python-standard:fix/generic-property-ascii-strCopy head branch name to clipboard