textsearch-ja - textsearch_groonga: Use PGXS automatically on make.

Log Message:
-----------
Use PGXS automatically on make.
Adjusted to pg_am changes in 9.1dev.

Modified Files:
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textsearch_groonga:
Makefile (r1.6 -> r1.7)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/textsearch-ja/textsearch_groonga/Makefile?r1=1.6&r2=1.7)
textsearch_groonga.sql.c (r1.1 -> r1.2)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/textsearch-ja/textsearch_groonga/textsearch_groonga.sql.c?r1=1.1&r2=1.2)
textsearch_groonga/doc:
textsearch_groonga.html (r1.2 -> r1.3)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/textsearch-ja/textsearch_groonga/doc/textsearch_groonga.html?r1=1.2&r2=1.3)