correctly mount tmpfs as /tmp in recovery

The syntax of init's mount command changed in April 2008 but
recovery's init.rc was never updated, so recovery's /tmp has been on
the root fs all this time.  Fix.

Also add /system/bin to the PATH in recovery, which is handy for
debugging.

Change-Id: I39f7ae435a8ce3bad691e4b7c307db0bd8de1302