fixup! Change set_variable_name API to consume irep_idt

Author: romainbrenguier

src/solvers/prop/prop.h

@@ -87,7 +87,7 @@ class propt:public messaget, public prop_assignmentt
 
   // variables
   virtual literalt new_variable()=0;
-  virtual void set_variable_name(literalt a, const std::string &name) { }
+  virtual void set_variable_name(literalt a, const irep_idt &name) { }
   virtual size_t no_variables() const=0;
   bvt new_variables(std::size_t width);