Offer "docx" as an option in `org-export-odt-preferred-output-format'

* org-odt.el (org-export-odt-convert-capabilities): Change the
default value.

See http://lists.gnu.org/archive/html/emacs-orgmode/2012-02/msg00293.html.

lisp/org-odt.el

@@ -2454,19 +2454,19 @@ from `org-export-odt-convert-processes'."
 
 (defcustom org-export-odt-convert-capabilities
   '(("Text"
-     ("odt" "ott" "doc" "rtf")
-     (("pdf" "pdf") ("odt" "odt") ("xhtml" "html") ("rtf" "rtf")
-      ("ott" "ott") ("doc" "doc") ("ooxml" "xml") ("html" "html")))
+     ("odt" "ott" "doc" "rtf" "docx")
+     (("pdf" "pdf") ("odt" "odt") ("rtf" "rtf") ("ott" "ott") ("doc" "doc")
+      ("docx" "docx") ("html" "html")))
     ("Web"
-     ("html" "xhtml") (("pdf" "pdf") ("odt" "txt") ("html" "html")))
+     (("pdf" "pdf") ("odt" "odt") ("html" "html")))
     ("Spreadsheet"
-     ("ods" "ots" "xls" "csv")
-     (("pdf" "pdf") ("ots" "ots") ("html" "html") ("csv" "csv")
-      ("ods" "ods") ("xls" "xls") ("xhtml" "xhtml") ("ooxml" "xml")))
+     ("ods" "ots" "xls" "csv" "xlsx")
+     (("pdf" "pdf") ("ots" "ots") ("html" "html") ("csv" "csv") ("ods" "ods")
+      ("xls" "xls") ("xlsx" "xlsx")))
     ("Presentation"
-     ("odp" "otp" "ppt")
-     (("pdf" "pdf") ("swf" "swf") ("odp" "odp") ("xhtml" "xml")
-      ("otp" "otp") ("ppt" "ppt") ("odg" "odg") ("html" "html"))))
+     ("odp" "otp" "ppt" "pptx")
+     (("pdf" "pdf") ("swf" "swf") ("odp" "odp") ("otp" "otp") ("ppt" "ppt")
+      ("pptx" "pptx") ("odg" "odg"))))
   "Specify input and output formats of `org-export-odt-convert-process'.
 More correctly, specify the set of input and output formats that
 the user is actually interested in.