(gud-format-command): Rewrite.

(gud-format-command): Rewrite.

(gud-format-command): Use gud-last-last-frame if
gud-last-frame is nil.

(gud-mipsdbx-massage-args, gud-mipsdbx-marker-filter):
New functions for dbx support on Mips under Ultrix.
(gud-dbx-mips-p, gud-mipsdbx-marker-acc): New variables.
(dbx) If gud-dbx-mips-p is non-nil, overload above two functions
and initialize appropriate command strings for dbx.

(gud-common-init): Call substitute-in-file-name.

(dbx): Let `comint-prompt-regexp' not match more than one line.