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/common.h b/common.h
index 98ce868..6761159 100644
--- a/common.h
+++ b/common.h
@@ -90,4 +90,7 @@
 #define LOGD(...) do {} while (0)
+#define STRINGIFY(x) #x
+#define EXPAND(x) STRINGIFY(x)