* lisp/character-fold.el: Make compatible with lax-whitespace
(character-fold-to-regexp): Rework internals to play nice with
lax-whitespacing.
When the user types a space, we want to match the table entry for
?\s, which is generally a regexp like "[ ...]". However, the
`search-spaces-regexp' variable doesn't "see" spaces inside these
regexp constructs, so we need to use "\\( \\|[ ...]\\)" instead (to
manually expose a space).
Furthermore, the lax search engine acts on a bunch of spaces, not
on individual spaces, so if the string contains sequential spaces
like " ", we need to keep them grouped together like this:
"\\( \\|[ ...][ ...]\\)".