Tests: take into account a default format of xhtml

The xhtml format is always tested, regardless of the default format.
Without this, if the default format is xhtml, CMake gives an error
when trying to add the xhtml test because it was already added.

development/autotests/CMakeLists.txt

@@ -55,6 +55,8 @@ macro(getdefaultoutputformat filepath varname)
       set(found ${CMAKE_MATCH_1})
       if(found STREQUAL "default")
 	set(found "pdf" "pdf2" "pdf5")
+      elseif(found STREQUAL "xhtml")
+	set(found "") # we test xhtml regardless of default format
       endif()
       set(${varname} ${found})
       break()