[Templates] INCLUDE_PATH generators and NAMESPACE tweaks

[Andy Wardley]

I've implemented support for a dynamic INCLUDE_PATH using generator
subs and objects.  Changes, documentation and tests are in CVS.

A trivial example:

    my $tt2 = Template->new( {
        INCLUDE_PATH => [ '/foo', '/bar', 
                          sub { return [ '/ping', '/pong' ] } ],
    } );

I've also fixed a stupidity on my part in the implementation of the
NAMESPACE handlers (the namespace prefix now *doesn't* get spliced
off before being passed to the handler's ident, this is a Good Thing).
Thanks to Bryan for pointing this out.  Also in CVS.

I'll roll out another developer release with these changes RSN.

A