setup: Add default config for Xbox360 on Linux.

The Xbox360 controller is handled differently by different
operating systems, and the layout is different on Linux to Windows.
Detect the Linux layout and set some appropriate defaults.
Make vcproj release settings consistent

Max optimization settings for release that were derived from Eternity
are now effective for all 4 games. In addition, generate map files for
debugging purposes.
Add desktop entries for all the games, make the Setup launch generic

The same icon is used for all four games, even though it's designed to
resemble Doom's logo and looks a bit silly with all of them lined up.

Also the Setup Desktop Entry now only launches chocolate-setup, which
then prompts for the game to configure. This avoids cluttering up a
DE's Preferences menu, control panel, or however it will be displayed.
Ignore some more autogenerated files
Merge pull request #410 from chungy/desktop

Add desktop entries for all the games, make the Setup launch generic
Merge pull request #411 from chungy/ignore

Ignore some more autogenerated files
Move extern definitions for p_map.c to p_local.h

This fixes conflicting array sizes for the variable "spechit" as
reported in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=748393.

Fixes #414