Bug 2505: Enabled warnings in opac_ISBDdetail.pl, opac-modrequest.pl, and opac-tags_subject.pl.

Enabling warnings in these files did not generate any warnings in the logs when tested.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>

opac/opac-ISBDdetail.pl

@@ -42,6 +42,8 @@ the items attached to the biblio
 =cut
 
 use strict;
+use warnings;
+
 use C4::Auth;
 use C4::Context;
 use C4::Output;

opac/opac-modrequest.pl

@@ -23,6 +23,8 @@
 # Suite 330, Boston, MA  02111-1307 USA
 
 use strict;
+use warnings;
+
 use CGI;
 use C4::Output;
 use C4::Reserves;

opac/opac-tags_subject.pl

@@ -25,6 +25,8 @@ TODO :: Description here
 =cut
 
 use strict;
+use warnings;
+
 use C4::Auth;
 use C4::Context;
 use C4::Output;