Check_MK Werk 6964: Fixed matching of literal strings when C++11 regex engine is used.

ID: 6964 Title: Fixed matching of literal strings when C++11 regex engine is used. Component: Livestatus Level: 2 Class: Bug fix Version: 1.6.0i1 Livestatus and CMC can use one of two regex engines: Either then one from the C++11 standard library or the one from the RE2 library. Normal builds ship the latter, only a manually built Livestatus should ever use the former. Nevertheless, both should work, but the C++11 variant had a quoting bug, resulting in incorrect matching. This has been fixed.