Rename %before-definitions to %start-header and %after-definitions to

Rename %before-definitions to %start-header and %after-definitions to
%end-header.  Don't use these declarations to separate pre-prologue
blocks from post-prologue blocks.  Add new order-independent
declarations %before-header and %after-header as alternatives to the
traditional Yacc pre-prologue and post-prologue blocks.  Discussed at
<http://lists.gnu.org/archive/html/bison-patches/2006-06/msg00110.html>.
* NEWS (2.3+): Update for these changes.
* data/glr.c (b4_before_definitions): Update to...
(b4_start_header): ... this.
(b4_after_definitions): Update to...
(b4_end_header): ... this.
* data/glr.cc: Likewise.
* data/lalr1.cc: Likewise.
* data/yacc.c: Likewise.
* doc/bison.texinfo (The prologue): Update names, and replace remaining
prologue blocks with %*-header declarations.
(Calc++ Parser): Likewise.
(Bison Declaration Summary): Update names.
(Bison Symbols): Update description.
* src/parse-gram.y (PERCENT_AFTER_DEFINITIONS): Update to...
(PERCENT_END_HEADER): ... this.
(PERCENT_BEFORE_DEFINITIONS): Update to...
(PERCENT_START_HEADER): ... this.
(PERCENT_AFTER_HEADER, PERCENT_BEFORE_HEADER): New tokens.
(declaration): Update token names and m4 macro names.
When parsing %end-header and %start-header, invoke translate_code
before muscle_code_grow, and no longer set global booleans to remember
whether these declarations have been seen.
Parse new %after-header and %before-header.
* src/reader.c (before_definitions, after_definitions): Remove.
(prologue_augment): Accept a new bool argument to specify whether to
augment the pre-prologue or post-prologue.
* src/reader.h (before_definitions, after_definitions): Remove these
extern's.
(prologue_augment): Add new bool argument.
* src/scan-gram.l (PERCENT_AFTER_DEFINITIONS): Update to...
(PERCENT_END_HEADER): ... this.
(PERCENT_BEFORE_DEFINITIONS): Update to...
(PERCENT_START_HEADER): ... this.
(PERCENT_AFTER_HEADER, PERCENT_BEFORE_HEADER): New tokens.
* tests/actions.at (Printers and Destructors): Update names.