[poppler] Warnings in the glib/cairo sides

[Albert Astals Cid]

gcc 4.6 gives

glib/poppler-attachment.cc:173:12:
	warning: variable ‘result’ set but not used [-Wunused-but-set-variable]

poppler/CairoFontEngine.cc:109:17:
	warning: variable ‘w3’ set but not used [-Wunused-but-set-variable]

poppler/CairoRescaleBox.cc:263:11:
	warning: variable ‘retval’ set but not used [-Wunused-but-set-variable]

Can you cairo/glib guys have a look at if we should be using them or if we can 
just kill them?

Thanks,
  Albert