Fix mutant_relation::operator=.

Defining

  template <bool FM>
  mutant_relation& operator=(const mutant_relation<TA, TB, Info, FM>& rel) {
    base_::change_to(rel);
    return *this;
  }

does not prevent the compiler from implicitly providing

  mutant_relation& operator=(const mutant_relation&);

and hence the implicit version takes over when FM == force_mutable and
does not call base_::change_to.

Replace the template version with two non-template overloads, both
calling base_::change_to.

Signed-off-by: Ignacy Gawędzki <[email protected]>

include/boost/bimap/relation/mutant_relation.hpp

@@ -289,8 +289,14 @@ class mutant_relation : public
 
     // Operators
 
-    template< bool FM >
-    mutant_relation& operator=(const mutant_relation<TA,TB,Info,FM> & rel)
+    mutant_relation& operator=(const mutant_relation & rel)
+    {
+	base_::change_to(rel);
+	return *this;
+    }
+
+    mutant_relation& operator=(const mutant_relation<TA,TB,Info,
+						     !force_mutable> & rel)
     {
         base_::change_to(rel);
         return *this;