anchor.diff:  
         CREATE FUNCTION [...]
                 AS '[..]liblwgeom', 'lwhistogram2d_in' LANGUAGE 'C' IMMUTABLE STRICT; -- WITH (isstrict);
  -    
  +
      where liblwgeom is the shared library.
      Postgis < 1.5 used absolute paths, in NixOS $libdir is always used.
   
      Thus if you want to use postgresql dumps which were created by non NixOS
      systems you have to adopt the library path.
  -
   
   
      ### TODO:
  
positive.code:   ### NixOS - usage:
    ==================
  
      services.posgresql.extraPlugins = [ pkgs.postgis.v_1_5_1 ];
  
      services.postgresql.extraPlugins = [ (pkgs.postgis.override { postgresql = pkgs.postgresql94; }).v_2_1_4 ];  # BM - 2015/01/01
  
      or if you want to install 1.5.x and 1.3.x at the same time (which works
      because the .sql and .so files have different names):
  
      services.postgis.extraPlugins = [ (pkgs.buildEnv {
            name = "postgis-plugins";
            ignoreCollisions = 1; # scripts will collide - but there are aliases with version suffixes
            paths = [ pkgs.postgis.v_1_3_5 pkgs.postgis.v_1_5_1 ];
          })];
  
      By now it is only supported installing one of the 1.3.x verions because
      their shared libraries don't differ in naming.
  
  
  
    ### important Postgis implementation details:
  
negative.code: 
  in rec {
  
    v_2_1_4 = pgDerivationBaseNewer.merge ( fix : {
      version = "2.1.4";
      sha256 = "1z00n5654r7l38ydkn2grbwl5gg0mravjwxfdipp7j18hjiw4wyd";
  