Add error mapping for unknown system variable.  Arrange for location tracing.
Add second exception hierarchy for checked mapped exceptions.  Rearrange the location
computation slightly.  Add known vars for have_dynamic_loading (default false for now),
version_compile_os (default "debian-linux-gnu") in order to help along mts.  Add the
ability for PEDDL to not load the named template if the template is preloaded.
Merge branch 'master' into kanzaros_eh