Enhance/fix VMS ONESHELL implementation and command execution

* job.c, vmsjobs.c: fix some double quote and new line handling;
implement ONESHELL with writing multiple lines into one DCL command
procedure; in ONESHELL allow VMS/make internal redirection only on the
first line; fix the created DCL command procedure, which didn't abort
on errors; return correct exit status from the DCL command procedure;
preserve current procedure verification; make the generated command
procedure more robust.
2 files changed