Method StringHolder

ext/catch.hpp:3309–3309

            template<typename MatcherT>
            struct StringHolder : MatcherImpl<MatcherT, NSString*>{
                StringHolder( NSString* substr ) : m_substr( [substr copy] ){}
                StringHolder( StringHolder const& other ) : m_substr( [other.m_substr copy] ){}
                StringHolder() {
                    arcSafeRelease( m_substr );