xmlto: add TEST with "make check", add cmd:cmp to BUILD_PREREQUIRES.

cmd:cmp is required for running "make check".
While at it, also sorted BUILD_PREREQUIRES alphabetically.

app-text/xmlto/xmlto-0.0.26.recipe

@@ -33,10 +33,11 @@ BUILD_REQUIRES="
 	haiku_devel
 	"
 BUILD_PREREQUIRES="
-	cmd:gcc
 	cmd:awk
-	cmd:getopt
+	cmd:gcc
+	cmd:cmp
 	cmd:flex
+	cmd:getopt
 	cmd:make
 	"
 
@@ -50,3 +51,8 @@ INSTALL()
 {
 	make install
 }
+
+TEST()
+{
+	make check
+}