Previously we produced a raster image, then multiplied image width
by DPI to get the page size. However if there is rounding the
page size may not match exactly. In this modified approach we
constrain the page size to match.
Breaks tests/test_main.py::test_tesseract_missing_tessdata because
conftest.py does not update options.tesseract_env before testing options
for some reason, and tesseract.has_textonly_pdf raises an exception
instead of returning False as the test assumes.
