RECOVERY_PRE_COMMAND_CLEAR_REASON and extended reboot arguments

fix the 2 new warnings created by our 4-lines recovery patch ;p

Allow also to override toolbox reboot applet, for bootmenu

Conflicts:
	libcutils/Android.mk
	libcutils/android_reboot.c
	toolbox/Android.mk

Change-Id: I2bff30b5f911e7b9ba8f26593523368223b12814