Rename <!> to <>. Discussed starting at

Rename <!> to <>.  Discussed starting at
<http://lists.gnu.org/archive/html/bison-patches/2006-11/msg00039.html>.
* NEWS (2.3a+): Update.
* doc/bison.texinfo (Freeing Discarded Symbols, Bison Symbols):
Update.
* src/parse-gram.y (TYPE_TAG_NONE, generic_symlist_item): Implement.
* src/scan-gram.l (INITIAL): Implement.
* src/symlist.c (symbol_list_default_tagless_new): Update comment.
* src/symlist.h (symbol_list, symbol_list_default_tagless_new): Update
comment.
* tests/actions.at (Default tagless %printer and %destructor,
Default tagged and per-type %printer and %destructor,
Default %printer and %destructor are not for error or $undefined,
Default %printer and %destructor are not for $accept,
Default %printer and %destructor for mid-rule values): Update.
* tests/input.at (Default %printer and %destructor redeclared,
Unused values with default %destructor): Update.