Renable preConfigure for kernel builder. Actually needed by custom kernel

Linux kernel 2.6.29 (release) has a slightly changed Makefile. They now add the prefix for depmod. So in NixOS "make modules_install" fails on depmod. To fix it, our old '/-b \$(INSTALL_MOD_PATH) -r/d' should be replaced with '/-b \$(INSTALL_MOD_PATH)/d'.

svn path=/nixpkgs/trunk/; revision=14811

pkgs/os-specific/linux/kernel/builder.sh

@@ -3,6 +3,10 @@ source $stdenv/setup
 
 configurePhase=configurePhase
 configurePhase() {
+    if test -n "$preConfigure"; then 
+        eval "$preConfigure"; 
+    fi
+
     export INSTALL_PATH=$out
     export INSTALL_MOD_PATH=$out