'make install DESTDIR=$pkgdir' is used when packaging modules. The
DESTDIR option installs the distribution into the given directory
preserving the directory structure. The packager then compresses
the directory with the added package information.

When using DESTDIR, the Makefile is unable to load XML::SAX in order
to update the ParserDetails.ini file because the DESTDIR is not in @INC
and the perl interpreter cannot find XML/SAX.pm.

This patch allows the Makefile to guess where the XML/SAX.pm file
will end up and adds this directory to @INC using the -I perl switch.

I have also switched to the single-quote heredoc because escaping all
of the $'s and @'s was annoying.

Replacing the install :: rule's text was unnecessary. Because it is
a double-color rule it can appear more than once.

I added some simple Makefile logic that will store the expected
destination of XML/SAX.pm in a make variable ("XMLSAXINC") depending
on which INSTALLDIRS are given. When packaging I set INSTALLDIRS to
vendor but the default is site. I am not aware of alternatives.
---
 Makefile.PL |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/Makefile.PL b/Makefile.PL
index 98928b3..dda94ac 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -38,11 +38,21 @@ sub MY::install {
     }
     
     if ($write_ini_ok) {
-        $script =~ s/install :: (.*)$/install :: $1 install_sax_pureperl/m;
-        $script .= <<"INSTALL";
+        $script .= <<'INSTALL';
+
+install :: install_sax_pureperl
+
+ifeq ($(INSTALLDIRS),site)
+XMLSAXINC = $(DESTINSTALLSITELIB)
+else ifeq ($(INSTALLDIRS),vendor)
+XMLSAXINC = $(DESTINSTALLVENDORLIB)
+else
+$(error Failed to detect destination. Unknown INSTALLDIRS: $(INSTALLDIRS))
+endif
 
 install_sax_pureperl :
-\t\@\$(PERL) -MXML::SAX -e "XML::SAX->add_parser(q(XML::SAX::PurePerl))->save_parsers()"
+	@$(PERL) -I$(XMLSAXINC) -MXML::SAX \
+	  -e "XML::SAX->add_parser(q(XML::SAX::PurePerl))->save_parsers()"
 
 INSTALL
 
-- 
1.7.3