[gnome-nibbles] Fix check for appdata- and desktop-file-validate - from Michael Catanzaro If these programs are not

[Bryan Quigley <bryanquigs src gnome org>]

commit e773c4bb961859d31801d3fd916300b858a83d53
Author: Bryan Quigley <bryanquigs src gnome org>
Date:   Mon Nov 4 18:04:02 2013 -0500

    Fix check for appdata- and desktop-file-validate - from Michael Catanzaro
    If these programs are not installed, do not try to use them. They're certainly nice for catching errors, 
but a developer who wants to use these tools will surely have them installed.

 configure.ac     |    3 +++
 data/Makefile.am |    4 ++++
 2 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 2fa64e2..f66632c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -72,7 +72,10 @@ PKG_CHECK_MODULES(GNOME_NIBBLES, [
 ])
 
 AC_PATH_PROG(APPDATA_VALIDATE, appdata-validate)
+AM_CONDITIONAL([VALIDATE_APPDATA], [test -n "${APPDATA_VALIDATE}"])
+
 AC_PATH_PROG(DESKTOP_FILE_VALIDATE, desktop-file-validate)
+AM_CONDITIONAL([VALIDATE_DESKTOP_FILE], [test -n "${DESKTOP_FILE_VALIDATE}"])
 
 dnl ###########################################################################
 dnl Internationalization
diff --git a/data/Makefile.am b/data/Makefile.am
index c653acf..5baef4e 100644
--- a/data/Makefile.am
+++ b/data/Makefile.am
@@ -43,7 +43,11 @@ install-exec-hook:
        fi
 
 check-local: $(appdata_DATA) $(desktop_DATA)
+if VALIDATE_APPDATA
        $(APPDATA_VALIDATE) $(appdata_DATA)
+endif
+if VALIDATE_DESKTOP_FILE
        $(DESKTOP_FILE_VALIDATE) $(desktop_DATA)
+endif
 
 -include $(top_srcdir)/git.mk