plugged the extension of the engine with python defined functions added a

* python/libxlst.c python/libxslt-python-api.xml
  python/libxsltclass.txt: plugged the extension of the engine
  with python defined functions
* python/tests/Makefile.am python/tests/extfunc.py: added a
  basic test, still a memleak, cleanup function needed.
Daniel

python/tests/extfunc.py

@@ -0,0 +1,49 @@
+#!/usr/bin/python -u
+import sys
+import libxml2
+import libxslt
+
+# Memory debug specific
+libxml2.debugMemory(1)
+
+def f(str):
+    import string
+    return string.upper(str)
+
+libxslt.registerExtModuleFunction("foo", "http://example.com/foo", f)
+
+styledoc = libxml2.parseDoc("""
+<xsl:stylesheet version='1.0'
+  xmlns:xsl='http://www.w3.org/1999/XSL/Transform'
+  xmlns:foo='http://example.com/foo'
+  xsl:exclude-result-prefixes='foo'>
+
+  <xsl:template match='/'>
+    <article><xsl:value-of select='foo:foo(\"foo\")'/></article>
+  </xsl:template>
+</xsl:stylesheet>
+""")
+style = libxslt.parseStylesheetDoc(styledoc)
+doc = libxml2.parseDoc("<doc/>")
+result = style.applyStylesheet(doc, None)
+style = None
+doc.freeDoc()
+
+root = result.children
+if root.name != "article":
+    print "Unexpected root node name"
+    sys.exit(1)
+if root.content != "FOO":
+    print "Unexpected root node content, extension function failed"
+    sys.exit(1)
+
+result.freeDoc()
+
+# Memory debug specific
+libxslt.cleanupGlobals()
+libxml2.cleanupParser()
+if libxml2.debugMemory(1) == 0:
+    print "OK"
+else:
+    print "Memory leak %d bytes" % (libxml2.debugMemory(1))
+    libxml2.dumpMemory()