MFC r340385 (by emaste):

strings: enter capability mode when operating on stdin

Reviewed by: oshogbo
Sponsored by: The FreeBSD Foundation

MFC r340391 (by emaste):

Revert r340385, strings capability mode

This needs to be reworked for bootstrapping.

(This is a record-only merge, so these revisions no longer show up in
"svn mergeinfo --show-revs=eligible" output.)