added dumpdir and truncate tasks

Job-configuration.md

@@ -108,6 +108,13 @@ test will fail anyway.
   and require at least one argument. For each provided one will be called
   [boost::filesystem::remove_all](http://www.boost.org/doc/libs/1_60_0/libs/filesystem/doc/reference.html#remove_all)
   command.
+- **Dumpdir task** copies a directory (usually a test directory, for debugging
+  purposes) recursively, with a limit on the total size of the destination
+  directory. Files that do not fit into the limit are skipped and
+  placeholders (with names like `original_file_name.skipped`) are created.
+- **Truncate task** cuts off data from the end of a file so that it fits a limit
+  supplied as an argument. This is done in place, using
+  [boost::filesystem::resize_file](http://www.boost.org/doc/libs/1_60_0/libs/filesystem/doc/reference.html#resize_file).
 
 ### External tasks