Fix bug with making [] extended alphabetic.

Fix bug with making [] extended alphabetic.

char-set/atom-delimiters must be changed in the parser to exclude [].
Otherwise the parser goes into an infinite loop since when peeking any
of them, we will read until a delimiter is found, but it will work as
a delimiter, so the empty string will be interned, and we will
dispatch on the peeked char again, ...