message: Symlink: Test copy.
diff: @@ -6,10 +6,19 @@ import drake
  from utils import *
  with Drake() as d:
  - source = drake.touch('source')
  + source = drake.write('content', 'source')
  s = drake.Symlink('link', source)
  ss = drake.Symlink('sub/link', source)
  s.build()
  assertEq(os.readlink('link'), 'source')
  ss.build()
  assertEq(os.readlink('sub/link'), '../source')
  + c = drake.copy(s, 'copied')
  + c.build()
  + assert not os.path.islink('copied/link')
  + with open('copied/link', 'r') as f:
  + assertEq(f.read(), 'content')
  + sc = drake.copy(s, 'scopied', follow_symlinks = False)
  + sc.build()
  + assert os.path.islink('scopied/link')
  + assertEq(os.readlink('scopied/link'), 'source')
  