Use .markdown instead of .mdwn as GitHub doesn't recognize the latter

SUPPORT.markdown

@@ -9,8 +9,8 @@ If these are not sufficient resources please consider posting any
 queries you might have to the [mailing
 list](http://xen-tools.org/software/xen-tools/lists.html)
 
-Included with the release you should find the file `BUGS.mdwn` which
-contains some notes on reporting bugs.
+Included with the release you should find the file `BUGS.markdown`
+which contains some notes on reporting bugs.
 
 
 Xen Queries

TODO.markdown

@@ -1,7 +1,7 @@
 TODO
 ====
 
-See KNOWN_BUGS.mdwn for real bugs.
+See KNOWN_BUGS.markdown for real bugs.
 
 Bugs to fix and features to add for 4.3
 ---------------------------------------

debian/docs

@@ -1,7 +1,7 @@
 AUTHORS
-README.mdwn
-SUPPORT.mdwn
-BUGS.mdwn
-TODO.mdwn
-KNOWN_BUGS.mdwn
+README.markdown
+SUPPORT.markdown
+BUGS.markdown
+TODO.markdown
+KNOWN_BUGS.markdown
 NEWS