[PATCH] libvisio: Fix tests without tools

I'd like to submit an easy patch that fixes the tests when libvisio is built without tools (in that 
case it was missing librevenge-stream reference).

Regards,
Andreas Sturmlechner

--- a/configure.ac      2015-07-25 09:29:53.000000000 +0200
+++ b/configure.ac      2016-02-07 00:19:30.534383076 +0100
@@ -317,6 +317,9 @@
 )
 AS_IF([test "x$enable_tests" = "xyes"], [
     PKG_CHECK_MODULES([CPPUNIT], [cppunit])
+    PKG_CHECK_MODULES([REVENGE_STREAM],[
+        librevenge-stream-0.0
+    ])
 ], [])
 AC_SUBST([CPPUNIT_CFLAGS])
 AC_SUBST([CPPUNIT_LIBS])