Update namazu package to 2.0.18.

Overview of Changes in Namazu 2.0.18 - May 12, 2008

* Add 'Charset' directive.
* "charset" was added to "ContentType" of the example in
  conf/namazurc-sample.
* "charset" was added to the response header in Error messages for
  namazu.cgi.
* Add HTML, BODY tags in Error messages for namazu.cgi.
* '\'', '(', ')' is converted into "'", "(", ")"
  respectively.
* Add po/{de, pl}.po files. (But, it doesn't translate.)
* Change charset from SJIS to Shift_JIS in po/ja_SJIS.po.
* Change soname (LTVERSION 8:0:1)
* pltests/env.pl: The checked environment variable and version of
  the checked Perl module is added.
* pltests/mknmz-8.pl.in: The confirmation whether the index
  has been updated is added.
* pltests/namazu-cgi-12.pl.in: Add new test.
* tests/mknmz-9: Expand test file.
* filter/hnf.pl: Correspondence GRP and bug fix.
* conf/*.win32: Add new files.

(taca)