Fix Mantis 3075 : Upgrades libpng from 1.5.7 to 1.6.12

git-svn-id: svn://svn.icculus.org/fs2open@10963 387891d4-d844-0410-90c0-e4c51a9137d3
"Fix" gcc warnings in Control_config[]

warning: missing initializer for member 'config_item::BLAH'
[-Wmissing-field-initializers]

git-svn-id: svn://svn.icculus.org/fs2open@10964 387891d4-d844-0410-90c0-e4c51a9137d3
Fix mantis 3078 (From Yarn)

Don't set / reset unscaled screen area when rendering to texture
Also fix a pre-10844 bug where scaling down a cockpit gauge would
cause the gauge to be improperly clipped if it was close enough to the
right or bottom edge of the texture.

git-svn-id: svn://svn.icculus.org/fs2open@10965 387891d4-d844-0410-90c0-e4c51a9137d3