gnash: add new 0.8.7 version, based on gnash_trunk.bb in gnash's bzr

gnash: add new 0.8.7 version, based on gnash_trunk.bb in gnash's bzr

The gnash_trunk.bb was made by Rob Savoye with lot of help from me

This recipe contains the following changes:
*--disable-avm2 for speed,for now it's useless and only output debug messages:
<bwy> It disables AVM2, though as AVM2 code doesn't do much, it's no less compatible without it.
*added speex dependency to avoid bad includes issues such as :
  | CROSS COMPILE Badness: /usr/include in INCLUDEPATH: /usr/include/speex
*converted to correct variables(${STAGING_INCDIR}instead of
  ${STAGING_DIR_HOST}/usr/include)
*make gnash plugin rdepend on gnash because gnash plugin executes
  the standalone gnash player