byteify-strings: handle triple quoted strings if they are not docstrings
As with anything in this script, this is a best effort approach. Most of the
time, when a triple quoted string is assigned to something, it's not a
docstring.
byteify-strings: handle multi-line strings in _ensuresysstr
The current implementation did not handle calls like
`repo.ui.log("first line"
"other line")`
correctly.