Properly make some methods const.

These had const at the beginning of the declaration, so it applied to
the return value rather than the object the method was being called on.

service_scan.h

@@ -268,7 +268,7 @@ class ServiceProbe {
   void setRarity(const char *portstr, int lineno);
 
   // Simply returns the rarity of this probe
-  const int getRarity() { return rarity; }
+  int getRarity() const { return rarity; }
 
   // Takes a match line in a probe description and adds it to the
   // list of matches for this probe.  This function should be passed