add back install target to the makefile

Just for compatibility with automation that did "make install".
diff --git a/tools/munger/Makefile b/tools/munger/Makefile
index dc5bf1c..06cc18d 100644
--- a/tools/munger/Makefile
+++ b/tools/munger/Makefile
@@ -40,6 +40,8 @@
 
 all: ${GEN_FILES}
 
+install: all
+
 # The core OpenFlow libraries generated from openflow.h
 ${TARGET_DIR}/cstruct.py: ${CSTRUCT_DEP}
 	${CSTRUCT_GEN_CMD} > ${CSTRUCT_AUX_INFO}