libsoup-2.4: add unstable version 2.37.2 which is needed for newer webkit-efl

* otherwise random runtime crashes can happen, see:
  https://lists.webkit.org/pipermail/webkit-efl/2011-December/000091.html


* this recipe should be removed as soon as there is 2.38 or newer
  version in oe-core
* newer libsoup-2.4 wasn't used because those depend also on unstable
  glib

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>