Sync past images

[bjones1]

preview sync fails after an image appears in the HTML. One example:

    @requiresModule('docutils')
    @base.inMainLoop
    def test_sync12(self):
        """Tables with an embedded image cause findText to fail.
        """
        self._textToWeb('table', """
================  ========================
header1           header2
================  ========================
img               .. image:: img.png
text after img    text after img
================  ========================

text after table""", False)

Add more examples (such as one without tables), fix (JavaScript to walk the DOM), test.