ENH: More informative error message if mysqldump cannot be found.

utils/patch_header.sh

@@ -131,6 +131,10 @@ function update_version {
 }
 
 function dump_table {
+    if [[ -z $MYSQLDUMP_CMD ]]; then
+        echo "Cannot find mysqldump program!" >&2
+        exit 2
+    fi
     $MYSQLDUMP_CMD $(get_db_args_nodb) $DATABASE_NAME $1 \
                     > ${DATABASE_NAME}.${1}.${OLD_VERSION}.dump.sql
 }