optimize utils::strmatch() by using const string reference

src/utils.cpp

@@ -82,7 +82,7 @@ using namespace LAMMPS_NS;
  *  even with char * type variables.
  *  Example: utils::strmatch(text, std::string("^") + charptr)
  */
-bool utils::strmatch(std::string text, std::string pattern)
+bool utils::strmatch(const std::string &text, const std::string &pattern)
 {
   const int pos = re_match(text.c_str(),pattern.c_str());
   return (pos >= 0);

src/utils.h

@@ -35,7 +35,7 @@ namespace LAMMPS_NS {
      *  \param pattern the search pattern, which may contain regexp markers
      *  \return true if the pattern matches, false if not
      */
-    bool strmatch(std::string text, std::string pattern);
+    bool strmatch(const std::string &text, const std::string &pattern);
 
     /** \brief Send message to screen and logfile, if available
      *