Avoid just-in-time compilation when not needed * inst/private/check_hash.m: check whether the previous compilation used the same ufl file * inst/private/save_hash.m: save to disk ufl file's md5sum for future comparison * inst/private/check_oct_files.m: ensure the expected oct files are present * inst/import_ufl_*.m: add checks using the logic above

1) Improve the feval
2) Add the possibility to use the 'normal' for BC
3) Add wrapper for subdomain (It should be enough to modify SubSpace)