Added cleanup of dev directory in Makefile

Makefile

@@ -69,7 +69,7 @@ export URL = http://www.libpng.org/pub/png/libpng.html
 REPO = main
 BRIEF = libpng is the official PNG reference library
 DESC = libpng is the official PNG reference library
-SNAPVER = 0
+SNAPVER = 1
 
 ARCHIVE := $(PWD)/SRC/$(shell ls SRC|egrep '(bz2|gz|tar|xz)$$'|tail -1)
 TYPE := $(shell file -ib $(ARCHIVE)|cut -d';' -f1|tr -d '\n')
@@ -143,6 +143,7 @@ test: $(ROOT)
 
 clean:
 	@rm -rvf $(ROOT) \
+		$(DEV) \
 		$(SNAPINFO) \
 		$(MANIFEST) \
 		$(FILES) \