ledger: requires an older boost

pkgs/top-level/all-packages.nix

···
 
   boost155 = callPackage ../development/libraries/boost/1.55.nix { };
   boost159 = callPackage ../development/libraries/boost/1.59.nix { };
+  boost15x = boost159;
   boost160 = callPackage ../development/libraries/boost/1.60.nix { };
   boost162 = callPackage ../development/libraries/boost/1.62.nix { };
   boost163 = callPackage ../development/libraries/boost/1.63.nix { };
   boost164 = callPackage ../development/libraries/boost/1.64.nix { };
+  boost16x = boost164;
   boost = boost162;
 
   boost_process = callPackage ../development/libraries/boost-process { };
···
   linuxband = callPackage ../applications/audio/linuxband { };
 
   ledger2 = callPackage ../applications/office/ledger/2.6.3.nix { };
-  ledger3 = callPackage ../applications/office/ledger { };
+  ledger3 = callPackage ../applications/office/ledger {
+    boost = boost15x;
+  };
   ledger = ledger3;
   ledger-web = callPackage ../applications/office/ledger-web { };