[iagno] Use a nicer check for *-validate and gtester

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 882df0813e957d4f3b73f18e291f073fe0b37e8b
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Tue Nov 5 19:24:50 2013 -0600

    Use a nicer check for *-validate and gtester

 configure.ac |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 4d92911..853e568 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,9 +25,12 @@ PKG_CHECK_MODULES(IAGNO, [
   libcanberra-gtk3 >= $CANBERRA_GTK_REQUIRED
 ])
 
-AC_PATH_PROG(APPDATA_VALIDATE, appdata-validate)
-AC_PATH_PROG(DESKTOP_FILE_VALIDATE, desktop-file-validate)
-AC_PATH_PROG(GTESTER, gtester)
+AC_PATH_PROG([APPDATA_VALIDATE], [appdata-validate], [/bin/true])
+AC_PATH_PROG([DESKTOP_FILE_VALIDATE], [desktop-file-validate], [/bin/true])
+AC_PATH_PROG([GTESTER], [gtester])
+if ! test -x "${GTESTER}" ; then
+  AC_MSG_ERROR([Please install gtester])
+fi
 
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 dnl Internationalization