libcutils : reboot mount fix

On aries for eg, cache needs to be rw for the RECOVERY_PRE_COMMAND to
work because we write to /cache/.startrecovery

This patchset moves the RECOVERY_PRE_COMMAND prior to the remount.

Conflicts:
	libcutils/android_reboot.c

Change-Id: I4bd97517e00cdd117191d29b610e9623ad7d9255
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