set_metadata unnecessarily strict in Perl bindings

[Eric Wong]

Calls which expect automatic integer to string conversion no longer works with the SWIG Xapian.pm bindings:

my $num = 6; $xdb->set_metadata("key", $num);

The old Search::Xapian bindings worked fine, and most Perl users expect auto-conversion from integers to strings. It would be easier for Perl users to auto-convert numeric values to the string type. Thanks.

[Olly Betts]

I agree it's not very Perl-ish, but it is actually documented in the "COMPATIBILITY" section of Xapian.pm from the newer bindings:

This module is fussier about whether a passed scalar value is a string or
an integer than Search::Xapian, so e.g. C<Xapian::Query-E<gt>new(2001)> will fail
but the equivalent worked with Search::Xapian.  If C<$term> might not be a
string use C<Xapian::Query-E<gt>new("$term")> to ensure it is converted to a
string.  Whether explicit stringification is needed depends on whether the
scalar is marked as having a string representation by Perl; prior to Perl
5.36.0 retrieving the string value of an integer could set this flag, but
that's no longer the case in Perl 5.36.0 and later.  The simple rule is to
always explicitly stringify if the value might be numeric.

This behaviour isn't very Perlish, but is likely to be hard to address
universally as it comes from SWIG.  Let us know if you find particular places
where it's annoying and we can look at addressing those.