Executable to run on boot that removes old tzdata if needed

tzdatacheck is exec'd from init.rc early in boot just after /data is
mounted. It checks to make sure that the tz rule data in /data
is newer than the version in /system. If the data is older it is
deleted. This is to address problems with earlier tz rule updates
that occurred: after an OTA upgrade previous updates in /data
would override newer versions in the system partition.

Includes change to init.rc neccessary to run it at boot time. Other
changes are in external/selinux.

Bug: 19941636
Bug: https://code.google.com/p/android/issues/detail?id=35730
Change-Id: I7cc61e058424c856da88f11ff9b259f34cb39dc7