[libdmapsharing] Fix configure script to better detect if we should build Vala code

[W. Michael Petullo <wmpetullo src gnome org>]

commit dc7f7fcf10acd184bbfb359de50a1f1310d3366e
Author: W. Michael Petullo <mike flyn org>
Date:   Sat Aug 9 21:06:42 2014 -0400

    Fix configure script to better detect if we should build Vala code
    
    Signed-off-by: W. Michael Petullo <mike flyn org>

 configure.ac |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index cab9654..82baac1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -346,8 +346,9 @@ AM_CONDITIONAL(HAVE_VALAC, test -x "$VALAC")
 
 AC_PATH_PROG(VALA_GEN_INTROSPECT, vala-gen-introspect)
 AC_PATH_PROG(VAPIGEN, vapigen)
-AM_CONDITIONAL(BUILD_VAPI, test -n "$VALA_GEN_INTROSPECT" -a -n "$VAPIGEN")
-if test -n "$BUILD_VAPI" ; then
+dnl GOBJECT_INTROSPECTION_CHECK sets found_introspection.
+AM_CONDITIONAL(BUILD_VAPI, test -n "$VALA_GEN_INTROSPECT" -a -n "$VAPIGEN" -a xyes = x"$found_introspection")
+if ! test -n "$VALA_GEN_INTROSPECT" -a -n "$VAPIGEN" -a xyes = x"$found_introspection"; then
        AC_WARN([will not build vapi])
 fi