textproc/p5-XML-SAX: fix checksum mismatch for ParserDetails.ini

• The file %%SITE_PERL%%/XML/SAX/ParserDetails.ini is updated by ports that depending textproc/p5-XML-SAX.
• For example, textproc/p5-XML-SAX-Expat, textproc/p5-XML-Simple and textproc/p5-XML-LibXML append something to the .ini file.
• This causes checksum mismatch when executing pkg check -s textproc/p5-XML-SAX

The fix provides a pkg-install program to handle the file in post-install.

PR: 197011
Submitted by: Tatsuki Makino <tatsuki_makino@hotmail.com>
Reviewed by: John Hein, mat, Walter Schwarzenfeld <w.schwarzenfeld@utanet.at>