Add a scripting hook variable that specifies the mouse buttons.
This variable is named MouseButton and is a bit field which uses the MOUSE_* defines (index 0 for right, 1 for left, 2 for middle).

git-svn-id: svn://svn.icculus.org/fs2open@10477 387891d4-d844-0410-90c0-e4c51a9137d3
Trunk Sync r10476

git-svn-id: svn://svn.icculus.org/fs2open@10478 387891d4-d844-0410-90c0-e4c51a9137d3
Adds SDL2main.lib to linking for SSE2 Debug/Release builds.

git-svn-id: svn://svn.icculus.org/fs2open@10479 387891d4-d844-0410-90c0-e4c51a9137d3