dist: add .exe extension to tour.exe
dist: add .exe extension to tour.exe

Fixes issue 5246.

R=golang-dev, dsymonds
CC=golang-dev
https://codereview.appspot.com/8558044

dsriram/golang,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,dsriram/golang,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,gnanderson/go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,apparentlymart/golang,apparentlymart/golang,dsriram/golang,tv42/old-go,dsriram/golang,dsriram/golang,gnanderson/go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,gnanderson/go