s4-python: only install external python libs that are missing

source4/script/installmisc.sh

@@ -83,6 +83,12 @@ cp setup/dns_update_list $SETUPDIR || exit 1
 
 echo "Installing external python libraries"
 mkdir -p $PYTHONDIR/samba_external || exit 1
-cp -r scripting/python/samba_external/* $PYTHONDIR/samba_external/ || exit 1
+for p in $($PYTHON scripting/python/samba_external/missing.py);
+do
+  echo "Installing missing python library $p"
+  mkdir -p $PYTHONDIR/samba_external/$p
+  cp -r scripting/python/samba_external/$p/* $PYTHONDIR/samba_external/$p/ || exit 1
+done
+
 
 exit 0

source4/scripting/python/samba_external/missing.py

@@ -0,0 +1,12 @@
+#!/usr/bin/python
+
+# work out what python external libraries we need to install
+
+list = []
+
+try:
+    import dns.resolver
+except:
+    list.append("dnspython")
+
+print ' '.join(list)