[four-in-a-row] build: make *-validate optional

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 14271ca090fe7962a64868db3f28bdac2672e12f
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Tue Nov 5 20:21:12 2013 -0600

    build: make *-validate optional

 configure.ac |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 2dafe44..baafaa1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -24,8 +24,8 @@ PKG_CHECK_MODULES(FOUR_IN_A_ROW, [
   zlib
 ])
 
-AC_PATH_PROG(APPDATA_VALIDATE, appdata-validate)
-AC_PATH_PROG(DESKTOP_FILE_VALIDATE, desktop-file-validate)
+AC_PATH_PROG([APPDATA_VALIDATE], [appdata-validate], [/bin/true])
+AC_PATH_PROG([DESKTOP_FILE_VALIDATE], [desktop-file-validate], [/bin/true])
 
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