[2433] constify various callback objects for consistency

src/lib/dns/master_loader.cc

@@ -393,7 +393,7 @@ private:
     shared_ptr<Name> last_name_; // Last seen name (for INITAL_WS handling)
     const RRClass zone_class_;
     MasterLoaderCallbacks callbacks_;
-    AddRRCallback add_callback_;
+    const AddRRCallback add_callback_;
     boost::scoped_ptr<RRTTL> default_ttl_; // Default TTL of RRs used when
                                            // unspecified.  If NULL no default
                                            // is known.

src/lib/dns/master_loader_callbacks.h

@@ -100,7 +100,7 @@ public:
     /// If the caller of the loader wants to abort, it is possible to throw
     /// from the callback, which aborts the load.
     void error(const std::string& source_name, size_t source_line,
-               const std::string& reason)
+               const std::string& reason) const
     {
         error_(source_name, source_line, reason);
     }
@@ -117,7 +117,7 @@ public:
     /// may be false positives), it is possible to throw from inside the
     /// callback.
     void warning(const std::string& source_name, size_t source_line,
-                 const std::string& reason)
+                 const std::string& reason) const
     {
         warning_(source_name, source_line, reason);
     }
@@ -133,7 +133,7 @@ public:
     static MasterLoaderCallbacks getNullCallbacks();
 
 private:
-    IssueCallback error_, warning_;
+    const IssueCallback error_, warning_;
 };
 
 }

src/lib/dns/rrcollator.cc

@@ -42,7 +42,7 @@ public:
                const RdataPtr& rdata);
 
     RRsetPtr current_rrset_;
-    AddRRsetCallback callback_;
+    const AddRRsetCallback callback_;
 };
 
 namespace {