This commit is just a slight modification (renaming and some small
changes) of the patch that has been provided by Andrey Hristov.
It adds support for hooking of the json parser operations and
allows re-using of modified JSON parsing outside of json ext.
The definitions file (json_parser.tab.h) contains file
system dependent name for C preprocessor guard:
YY_PHP_JSON_YY_HOME_JAKUB_PROG_PHP_MASTER_EXT_JSON_JSON_PARSER_TAB_H_INCLUDED
This is because the srcdir is used for default definitions name.
It's a correct default (--definition=$(srcdir)/json_parser.tab.h)
because the build would fail otherwise. Unfortunately Bison does not have
a special option for defining cpp guard name. The only way would be
using skeleton file but that's not possible with the current
configuration as it requires using a specific bison version
(disallowing range of supported versions).
