you could do that, but it adds a fair amount of awkwardness
into the lexer; i'm not sure that's justified. rc uses ~ instead of ^
for the same reason, which i would have done in the inferno
shell, except that i wished to re-use the existing filepat module.

an alternative might be to scan the pattern before passing
to filepat, substituting [~ by [^; it would be quite simple,
just add something like the following to patquote()

	if(word[i] == '[' && i < len word - 1 && word[i+1] == '~')
		word[i+1] = '^';

although that does potentially break some existing shell scripts
and it's not clear whether ['^'b] should continue to have
the same meaning.

i'll do this if there's a consensus...