pkgs/development/python-modules/generic: parameterize build/install command

The generic 'buildPythonPackage' function used to use the build/install command
"easy_install" unconditionally. That didn't work for python-numpy, for
instance, because the package wants "setup.py" run with additional parameters
to determine the fortran compiler of choice. The newly introduced function
argument 'installCommand' allows to implement this. By passing that parameter,
the default build command can be overridden.

svn path=/nixpkgs/trunk/; revision=22786

pkgs/development/python-modules/generic/default.nix

@@ -6,11 +6,14 @@
 { python, setuptools, makeWrapper, lib }:
 
 { name, namePrefix ? "python-", src, meta, patches ? []
+, installCommand ? ""
 , doCheck ? true, checkPhase ? "python setup.py test"
 , postInstall ? ""
 , ... } @ attrs:
 
 let
+    defaultInstallCommand = ''easy_install --prefix="$out" .'';
+
     # Return the list of recursively propagated build inputs of PKG.
     recursiveBuildInputs =
       pkg:
@@ -50,7 +53,7 @@ python.stdenv.mkDerivation (
 
     echo "installing \`${name}' with \`easy_install'..."
     export PYTHONPATH="$out/lib/${python.libPrefix}/site-packages:$PYTHONPATH"
-    easy_install --prefix="$out" .
+    ${if installCommand == "" then defaultInstallCommand else installCommand}
 
     ${postInstall}
   '';