* gash/compat.scm [mes] (X_OK): New variable.
[mes] (program-arguments): New procedure.
[mes] (delete-duplicates!): New procedure.
[mes] (flush-all-ports): New procedure.
[mes] (file-port?): New procedure.
[mes] (input-port?): New procedure.
[mes] (output-port?): New procedure.
[mes] (dup): Redefine to support an optional 'new' argument.