Issue 4550: Avoid "using namespace std;" in included files (Take 2)

lily/paper-column.cc

Index: lily/paper-column.cc
diff --git a/lily/paper-column.cc b/lily/paper-column.cc
index c428414e66a83bbb0617f0ab1768baa391e30f8d..6fc65f27614e3c16cdf63766ee3642514b0afea6 100644
--- a/lily/paper-column.cc
+++ b/lily/paper-column.cc
@@ -39,6 +39,9 @@
 #include "text-interface.hh"
 #include "warn.hh"
 
+using std::string;
+using std::vector;
+
 bool
 Paper_column::internal_set_as_bound_of_spanner (Spanner *s, Direction)
 {
@@ -155,7 +158,7 @@ Paper_column::minimum_distance (Grob *left, Grob *right)
 
   skys[RIGHT].merge (Separation_item::conditional_skyline (right, left));
 
-  return max (0.0, skys[LEFT].distance (skys[RIGHT]));
+  return std::max (0.0, skys[LEFT].distance (skys[RIGHT]));
 }
 
 Interval