proton: Call python3 explicitly on Linux

Frustratingly, Ubuntu ships no python binary by default, only python3,
so we can't just call python and expect it to work. This will fail on
distros that don't ship python3, but them's the breaks.

build_proton.sh

@@ -672,13 +672,16 @@ if [ "$PACKAGE" = true ]; then
 
     cp -a toolmanifest.vdf dist/
     cp -a filelock.py dist/
-    cp -a proton dist/
     cp -a user_settings.sample.py dist/
     if [ "$PLATFORM" == "Darwin" ]; then
-    cp -a dist.LICENSE.osx dist/LICENSE
+        cp -a dist.LICENSE.osx dist/LICENSE
+        sed -e 's/@PYTHON_NAME@/python/' proton.in > dist/proton
     else
-    cp -a dist.LICENSE.lin dist/LICENSE
+        cp -a dist.LICENSE.lin dist/LICENSE
+        #work around Ubuntu 18.04 failing to ship a python by default
+        sed -e 's/@PYTHON_NAME@/python3/' proton.in > dist/proton
     fi
+    chmod 755 dist/proton
     date '+%s' > dist/version
 
     echo "Proton ready in dist/"

proton.in

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env @PYTHON_NAME@
 
 #script to launch Wine with the correct environment
 
@@ -509,3 +509,5 @@ else:
     sys.exit(1)
 
 sys.exit(0)
+
+# vim: set syntax=python:

user_settings.sample.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 #to enable these settings, name this file "user_settings.py"
 
 user_settings = {