Revert "new scalable contentpane does not work for jdk < 8"

This reverts commit d9a2e9136a91c5a77bd28914538137e023ea0df2.
we found the code that causes trouble in jdk < 8, trying to fix it
added scalablecontentpane fix for jdk 7:
- content does not repaint if realHeight equals exactly the pref height of the contentpane
  thus, we add a very small value (0.001)