gdb pretty printer for SwNodes fails on Python 3 due to "unicode"

Change-Id: I8e4983a91d4f97a2a20fbeed89d4e0f186c35fad
(cherry picked from commit f29ac1d9)
Reviewed-on: https://gerrit.libreoffice.org/17373Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>

solenv/gdb/libreoffice/sw.py

@@ -213,7 +213,7 @@ class BigPtrArrayPrinter(object):
                 # accessing this is completely non-obvious...
                 # also, node.dynamic_cast(node.dynamic_type) is null?
                 value = "    TextNode " + \
-                  unicode(node.cast(node.dynamic_type).dereference()['m_Text'])
+                  six.text_type(node.cast(node.dynamic_type).dereference()['m_Text'])
             elif str(node.dynamic_type.target()) == "SwOLENode":
                 value = "     OLENode "
             elif str(node.dynamic_type.target()) == "SwGrfNode":