dot/gnus.el: Make `<' and `>' be punctuation when splitting mail.

dot/gnus.el: Make `<' and `>' be punctuation when splitting mail.

Email addresses are commonly written between angle brackets in header
lines.  I sometimes want to be able to parse out an entire email
address, or at least a local-part, from a header, as part of a Gnus
split specifier.  But Gnus prepends a `.*' to the split regexp, so one
needs to take special precautions to start in the right place, typically
by using `\_<' to align to the start of a symbol.  But if `<' is a
symbol character, then this won't work.

Worse, Gnus typically also tries to align to a word boundary by sneaking
in `\<'.  But then we have `\<\_<', which rejects an email address
starting enclosed in `<' ... `>' altogether.

Fortunately, the syntax table used by Gnus while splitting email is
configurable, so we can override this silliness.