Fix string search method in #532

Fix a bug that caused any egs++ application to crash immediately when
run. This happened due to a misuse of string method find_last_of instead
of method rfind to reverse-search for the ".exe" extension substring in
the application name.

HEN_HOUSE/egs++/egs_application.cpp

@@ -247,9 +247,9 @@ EGS_Application::EGS_Application(int argc, char **argv) : input(0), geometry(0),
  app_name = egsStripPath(argv[0]);
 
  // In Windows PowerShell, we need to remove a .exe extension
- size_t exePos = app_name.find_last_of(".exe");
+ size_t exePos = app_name.rfind(".exe");
  if (exePos != string::npos) {
- app_name = app_name.substr(0, exePos-3);
+ app_name = app_name.substr(0, exePos);
  }
  }
  if (!app_name.size()) egsFatal("%s\n failed to determine application "