Incorrect parsing of line continuation

[achudnov]

In Lexer's singleStringCharacter and doubleStringCharacter the lineContinuation is never parsed. The regression is isolated in "line-cont-string.js".

[achudnov]

Fixed in d029f05

[achudnov]

Still failing: 12.10.1-2-s.js
12.10.1-8-s.js
11.1.5_7-2-2-s.js
14.1-4-s.js

and others