fixed three bugs in the parser and pretty printer

Two of the bugs were passing the wrong accessor function to the pretty
printer.

The third bug was that the pretty printer rendered "foo\\bar" as
"foo\bar", but actually in order to get the slash into the string, the
user would have to have used the quote syntax.  I think we decided
that the quote syntax meant a haskell string, so they should input it
as "foo\\bar", of course internally represented as "foo\bar', but when
printed, it should show two slashes again.