logd: throttle SELinux denials to 20/sec

Impose a limit of 20 selinux denials per second. Denials beyond
that point don't add any value, and have the potential to cause
crashes or denial of service attacks.

Do some other misc cleanup while I'm here.

Bug: 18341932
Change-Id: I6125d629ae4d6ae131d2e53bfa41e1f50277d402
Modular backuptool.sh.  Executes backup and restore methods defined in arbitrary /system/addon.d/*.sh scripts.

Set permissions on /system/addon.d/ and files within.

Patch Series
============
http://review.cyanogenmod.com/#change,13265
CyanogenMod/android_build
  * edify generator
http://review.cyanogenmod.com/#change,13266
CyanogenMod/android_system_core
  * permissions on /system/addon.d
http://review.cyanogenmod.com/#change,13267
CyanogenMod/android_vendor_cm
  * 50-cm.sh reference backup script
  * modular backuptool.sh
  * support backuptool.functions used by /system/addon.d/*.sh scripts

Change-Id: I4f1464ea8d55f45d47ba760a7a448036a46feb00