ledger: Use Boost Python support if applicable

Since 772eef91686974b7710081a9a77e5c0e287c25e8 Boost no longer has
Python support enabled by default, so depending on whether Ledger has
Python support built in we also use either Boost with Python support or
without.

Tested building with and without Python support and both builds now
succeed.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @the-kenny, @jwiegley

pkgs/applications/office/ledger/default.nix

@@ -13,7 +13,10 @@ stdenv.mkDerivation rec {
     fetchSubmodules = true;
   };
 
-  buildInputs = [ boost gmp mpfr libedit python texinfo gnused ];
+  buildInputs = [
+    (boost.override { enablePython = usePython; })
+    gmp mpfr libedit python texinfo gnused
+  ];
 
   nativeBuildInputs = [ cmake ];