add clear_env option to FPM config

This makes it possible to leave the envoronment as is on startup and
pass all the variables to the workers.
The default value of clear_env is "yes", preserving previous behaviour.
Patch by Paul Annesley.
fixed macro
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  fixed macro
Merge branch 'PHP-5.5' into PHP-5.6

* PHP-5.5:
  fixed macro
Merge branch 'PHP-5.6'

* PHP-5.6:
  fixed macro
  add clear_env option to FPM config