base.bbclass: Fix oe_unpack_file to unpack files to match new bitbake bb.decodeurl()

base.bbclass: Fix oe_unpack_file to unpack files to match new bitbake bb.decodeurl()

* This patch now uses the path which essentially is the path and
  filename relative to recipe dir. It will create the directories
  as expected. Suppose if the is says file://pam.d/login in the
  SRC_URI then it will be copied to $WORKDIR/pam.d/login as it
  was happening before the fix to decodeurl in bitbake.

* Do not copy the .patch and .diff files into $WORKDIR
  they are already symlinked in patches/ dir which will
  be used by quilt.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Acked-by: Roman I Khimov <khimov@altell.ru>
Acked-by: Chris Larson <clarson@kergoth.com>