I just re-built gimp and verfied the screenshot problem is still there - a window appears titled "gimp message" but it is blank, so it is a little hard to figure out what's missing.
I did not compile against graphics-libs1, but I can't image the lack of tiff, gif or otherwise is the problem - I'll keep searching and also start thinking about gimp2...
Edit - I see the error now - "LibGimp-WARNING **: screenshot: wire_read: unexpected EOF" and "LibGimp-WARNING **: script-fu: wire_read: unexpected EOF". I feel this is something to do with perl (or the lack thereof...)
Edit2 - NOTICE: unable to use the Perl-Gtk interface. Many features (like
Gimp::Fu) rely on this extension. You can build without it (and
many scripts will be disabled or run with reduced functionality
only), but it's better to install it (version 0.6123 or higher is
required, you can get it from
ftp://ftp.gimp.org/pub/gtk/perl/ or
any CPAN mirror.
So - not only does the gimp-1.2.5 screenshot depend on perl, it also depends on a (large) perl module. I therefore vote to leave things as they are for now..