Linux64 build was segfaulting with the following error: "Program received signal SIGFPE, Arithmetic exception. 0x000000000047f352 in hx::Mod (inLHS=0, inRHS=0) at /usr/lib/haxe/lib/hxcpp/3,0,2//include/hx/Operators.h:93"
fixes #651: if you destroy() a FlxObject, set the exists flag to false
Negative offsets, and minimum positions were not calculated correctly
merge upstream/dev
Revert "Negative offsets, and minimum positions were not calculated correctly"

This reverts commit a3e460809a0111af45fd77d0501239677d786973.
This check was added, but not needed
Merge pull request #656 from ArtBIT/dev

Linux64 build segfault fix & destroying a FlxObject should set exists to false