let the "firmware" command take the file straight from the package

To do a firmware-install-on-reboot, the update binary tells recovery
what file to install before rebooting.  Let this file be specified as
"PACKAGE:<foo>" to indicate taking the file out of the OTA package,
avoiding an extra copy to /tmp.  Bump the API version number to
reflect this change.
diff --git a/Android.mk b/Android.mk
index 6ab498e..0367fef 100644
--- a/Android.mk
+++ b/Android.mk
@@ -22,6 +22,9 @@
 
 LOCAL_FORCE_STATIC_EXECUTABLE := true
 
+RECOVERY_API_VERSION := 2
+LOCAL_CFLAGS += -DRECOVERY_API_VERSION=$(RECOVERY_API_VERSION)
+
 # This binary is in the recovery ramdisk, which is otherwise a copy of root.
 # It gets copied there in config/Makefile.  LOCAL_MODULE_TAGS suppresses
 # a (redundant) copy of the binary in /system/bin for user builds.