K 10
svn:author
V 3
smh
K 8
svn:date
V 27
2016-01-21T15:27:44.325303Z
K 7
svn:log
V 996
Prevent loader.conf load failure due to unknown console entries

When processing loader.conf if console contained an entry for an unsupported
console then cons_set would return an error refusing to set any console.

This has two side effects:

1. Forth would throw a syntax error and stop processing loader.conf at that
  point.
2. The value of console is ignored.

#1 Means other important loader.conf entries may not be processed, which is
   clearly undesirable.
#2 Means the users preference for console aren't applied even if they did
   contain valid options. Now we have support for multi boot paths from a
   single image e.g. bios and efi mode the console preference needs to deal
   with the need to set preference for more than one source.

Fix this by:
* Returning CMD_OK where possible from cons_set.
* Allowing set with at least one valid console to proceed.

Reviewed by:	allanjude
MFC after:	1 week
Sponsored by:	Multiplay
Differential Revision:	https://reviews.freebsd.org/D5018

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