Fix #1494.
Fix #1494.

This fixes the catastrophic backtracking which previously occured for strings
like "\057hom\145/e2\071501\057pub\154ic_\150tml\057a

pygments/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,pygments/pygments,pygments/pygments,pygments/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,pygments/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,pygments/pygments,dscorbett/pygments,pygments/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments,pygments/pygments,dscorbett/pygments,dscorbett/pygments,dscorbett/pygments,dscorbett/pygments,pygments/pygments