We only use expect(...).toEval() / not.toEval() for checking syntax
errors, where we obviously can't put the code in a regular function. For
runtime errors we do exactly that, so toEval() should not fail - this
allows us to use undefined identifiers in syntax tests.
Newlines after line continuation were inserted into the string
literals. This patch makes the parser ignore the newlines after \ and
also makes it so that "use strict" containing a line continuation is
not a valid "use strict".
