website: configure.ac: check for sed.

In the Makefile we have the following:
    index.html: index.html.tmpl
            sed -e "s#WEBSITE_PREFIX#$(WEBSITE_PREFIX)#g" "$^" > "$@"
so we need to make sure that 'sed' is available.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>

website/configure.ac

@@ -90,6 +90,10 @@ AC_CHECK_PROG([FOUND_REALPATH], [realpath], [realpath])
 AS_IF([test x"$FOUND_REALPATH" = x""],
       [AC_MSG_ERROR([realpath was not found in PATH ($PATH)])])
 
+AC_CHECK_PROG([FOUND_SED], [sed], [sed])
+AS_IF([test x"$FOUND_SED" = x""],
+      [AC_MSG_ERROR([sed was not found in PATH ($PATH)])])
+
 AC_CHECK_PROG([FOUND_TAR], [tar], [tar])
 AS_IF([test x"$FOUND_TAR" = x""],
       [AC_MSG_ERROR([tar was not found in PATH ($PATH)])])