Revert "make RegexParser.err handle whitespace like literal and regex."

Reverts scala/scala-parser-combinators#30 (dc9e9cf), because it isn't binary compatible with `1.0.2`. Mima did catch it, this was human error (mine).

The plan is:
 - `1.0.3` gets released with this PR (so without the fix),
 - `master` becomes `1.1.0-SNAPSHOT` and the fix is reapplied. That version isn't binary compatible with the `1.0` versions, so it cannot be bundled with 2.11,
 - a `1.0.x` branches is created for a possible `1.0.4`, for binary compatible changes.