Convert (most of) the test data files into genuine XML. A handful still

are not, due mainly to the lack of support for XML character entities
(e.g. & => & ).  This will make it easier to validate test files using
tools like xmllint, as well as edit and view them using XML tools.

tests/data/test251

@@ -1,3 +1,4 @@
+<testcase>
 # Server-side
 <reply>
 # When doing LIST, we get the default list output hard-coded in the test
@@ -51,3 +52,4 @@ LIST
 QUIT
 </protocol>
 </verify>
+</testcase>