search: make the \b and \B anchors work correctly in both directions

That is: remove the special treatment of BOW anchors, and instead make
regexes match against the whole line instead of against an artificially
shortened one, because the latter method creates ghost matches: matches
at the starting point of the search that aren't really matches when seen
in the context of the whole line.

This fixes https://savannah.gnu.org/bugs/?50030.
2 files changed