Added remove lib directory and re-create it again to build_sdk to do a clean clean build

build_sdk.sh

@@ -1,4 +1,4 @@
 #!/bin/sh
 
-mkdir lib && cd ARDroneLib/Soft/Build && make clean && make && cp -f targets_versions/*/*.a ../../../lib/
+rm -rf ./lib && mkdir lib && cd ARDroneLib/Soft/Build && make clean && make && cp -f targets_versions/*/*.a ../../../lib/
 cd ../../../