* textmodes/flyspell.el (flyspell-highlight-incorrect-region):
Ignore the read-only property when flyspell highlighting is on.
Not ignoring it leads to a series of confusing errors.
(flyspell-highlight-duplicate-region): Ignore read-only, as above,
but also make sure to call flyspell-incorrect-hook.
(flyspell-maybe-correct-transposition): Perform transposition test
by bit twiddling a string, rather than using a temp buffer.
(flyspell-maybe-correct-doubling): Use a string rather than a temp
buffer. This is also the original version of the code, which
could not be checked in before due to a previous lack of
assignment papers. This version has seen heavy usage on my system
for several years now.
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