restrict abstract field access to :impl fields and those that unify (fixed issue #1410)

git-svn-id: http://haxe.googlecode.com/svn/trunk@5925 f16182fa-f095-11de-8f43-4547254af6c6
improved cast detection for dynamic types (fixed issue #1409)

git-svn-id: http://haxe.googlecode.com/svn/trunk@5926 f16182fa-f095-11de-8f43-4547254af6c6
export HAXE_LIBRARY_PATH (fixed issue #1411)

git-svn-id: http://haxe.googlecode.com/svn/trunk@5927 f16182fa-f095-11de-8f43-4547254af6c6