Add scons build to appveyor builds

This will guarantee we can build hammer with default arguments

appveyor.yml

@@ -1,9 +1,16 @@
 platform:
 - x86
 - x64
+environment:
+    PYTHON: "C:\\Python27"
 version: 1.0.{build}
 os: Visual Studio 2015
+install:
+  - SET "PATH=%PYTHON%;%PYTHON%\\Scripts;%PATH%"
+  - easy_install scons
 build_script:
+- scons --version
+- scons install
 - '@echo off'
 - setlocal
 - ps: >-