set method doesn't include user set timestamp if update set() is supposed to update the record with the key if it already exists. It does update the value marshalled data blob. However it doesn't update the timestamp column for rdbms tables if provided. This change updates the x_time column with the provided __timestamp or preserves the original timestamp.

try:
    from html import escape as html_escape_  # python 3

    def html_escape(str, quote=False):
        # html_escape under python 3 sets quote to true by default
        # make it python 2 compatible
        return html_escape_(str, quote=quote)
except ImportError:
    # python 2 fallback
    from cgi import escape as html_escape  # noqa: F401