[yelp-tools] yelp.m4: Make ITSTOOL and XMLLINT precious variables

[Shaun McCance <shaunm src gnome org>]

commit f4be0837bb5a2007b15e761dfdf34b5c88a90e4f
Author: Shaun McCance <shaunm gnome org>
Date:   Thu May 12 12:19:15 2011 -0400

    yelp.m4: Make ITSTOOL and XMLLINT precious variables

 tools/yelp.m4 |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/tools/yelp.m4 b/tools/yelp.m4
index 4dcd3dc..272659b 100644
--- a/tools/yelp.m4
+++ b/tools/yelp.m4
@@ -11,12 +11,14 @@ AC_ARG_WITH([help-dir],
 HELP_DIR="$with_help_dir"
 AC_SUBST(HELP_DIR)
 
-AC_CHECK_PROG(ITSTOOL, itstool, itstool)
+AC_ARG_VAR([ITSTOOL], [Path to the `itstool` command])
+AC_CHECK_PROG([ITSTOOL], [itstool], [itstool])
 if test x"$ITSTOOL" = x; then
   AC_MSG_ERROR([itstool not found])
 fi
 
-AC_CHECK_PROG(XMLLINT, xmllint, xmllint)
+AC_ARG_VAR([XMLLINT], [Path to the `xmllint` command])
+AC_CHECK_PROG([XMLLINT], [xmllint], [xmllint])
 if test x"$XMLLINT" = x; then
   AC_MSG_ERROR([xmllint not found])
 fi