[#291] Disable ObjectEntity falling flag when there is no gravity.
[#291] Disable ObjectEntity falling flag when there is no gravity.

- Thanks @Deathspike for #478

MarkoIvanetic/melonJS,srbala/melonJS,melonjs/melonJS,MarkoIvanetic/melonJS,melonjs/melonJS,gopalindians/melonJS,TukekeSoft/melonJS,TukekeSoft/melonJS,rlugojr/melonJS,srbala/melonJS,gopalindians/melonJS,rlugojr/melonJS,gopalindians/melonJS,rlugojr/melonJS,TukekeSoft/melonJS,srbala/melonJS