Fixed libxslt to check if python is actually available

Note:

It seems there are issues connected to the PYTHON environment variable,
leaking into the sandbox if python is installed on the system the target
is build on. Nevertheless it seems to be not a big problem it might be
safer to add this check!
The same problem also appears while building the libxml package!

textproc/libxslt/libxslt.conf

@@ -2,7 +2,7 @@
 # This copyright note is auto-generated by ./scripts/Create-CopyPatch.
 # 
 # Filename: package/.../libxslt/libxslt.conf
-# Copyright (C) 2007 The OpenSDE Project
+# Copyright (C) 2007 - 2008 The OpenSDE Project
 # 
 # More information can be found in the files COPYING and README.
 # 
@@ -16,10 +16,12 @@ if ! pkginstalled libgcrypt; then
 	var_append extraconfopt ' ' '--without-crypto'
 fi
 
-if ! atstage native; then
+if ! atstage native || ! pkginstalled python; then
 	# python, not on stage 1 please
 	var_append extraconfopt ' ' '--without-python'
+fi
 
+if ! atstage native; then
 	# help it to find the right libxml
 	var_append extraconfopt ' ' "--with-libxml-prefix=$root/$( pkgprefix libxml )"
 fi