Consolidate the exec/eval bits, switch anonfunc to better_exec, etc

Consolidate the exec/eval bits, switch anonfunc to better_exec, etc

The methodpool, ${@} expansions, anonymous python functions, event handlers
now all run with the same global context, ensuring a consistent environment
for them.  Added a bb.utils.better_eval function which does an eval() with the
same globals as better_exec.

(Bitbake rev: 424d7e267b009cc19b8503eadab782736d9597d0)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>