Eliminate excess whitesapce above labels & fix middle/tail truncation mixup

Change-Id: Iee17956bcceebb887b2dd9b19876a1515199da62
Merge pull request #288 from bkennyatmeetme/master

Eliminate excess whitesapce above labels & fix middle/tail truncation mixup
Workaround for 4" CATiledLayer bug on frame change. setNeedsDisplay does not dirty enough. Fixes #283
Improvements on content view
- added intrinsicContentSize as the place where the needed size is retrieved from layout frame
- this might be needed in places where Auto Layout needs to know the intrinsic size of the text
- not 100% certain of this, but better safe than sorry
- sizeThatFits also calls intrinsicContentSize now
- prevent creation of a layout frame if bounds+edge insets are negative or zero
- do not unnecessarily discard the layouter. It should only be necessary to do that if the attributed string changes.
Merge branch 'master' of github.com:minorblend/DTCoreText