(patch) displayobjects/line: Fix end positions when setting length

Setting the length property should resize the line around its
origin. This was broken in 2.4.0. Setting the x/y properties will
call the setter functions that will change some internal
properties that need to be correct when setPosition is called.
Add custom events support

Based on code by Dqubes and review by koggdal.
Merge pull request #87 from xrmx/customevents3

Add custom events support
Update version number to 2.5.0