warn on -copy=false

As discussed in http://goo.gl/RpYs8e, we will be
removing the ability to save dependencies without
copying their source code. Warn users now of this
upcoming change.
warn while reading deps if -copy=false was used

As discussed in http://goo.gl/RpYs8e, we will be
removing the ability to read dependencies without
source code. Warn users now of this upcoming change.
step 3: remove flag -copy=false
step 4: remove sandbox code