Revert "Fix for #2613, when using  php < 5.4 there was an unnecessary backslash before each utf-8 char.  The problem was that the regexp matched all utf-8 encoded chars (included the ones that where escaped). The new regexp uses the lookbehind feature to check if the backslash isn't prefixed with an other backslash."

This reverts commit 7a902ed96d3225817bc88f7a62db1f5ebb531e3c.