Add test for "pip install comtypes" (reproduce enthought#155).

appveyor.yml

@@ -24,3 +24,5 @@ environment:
 
 test_script:
    - C:\%py%\python.exe setup.py install
+   - C:\%py%\Scripts\pip.exe uninstall comtypes -y
+   - C:\%py%\python.exe test_pip_install.py

test_pip_install.py

@@ -0,0 +1,24 @@
+import os
+import sys
+import subprocess
+
+def read_version():
+    # Determine the version number by reading it from the file
+    # 'comtypes\__init__.py'.  We cannot import this file (with py3,
+    # at least) because it is in py2.x syntax.
+    ns = {}
+    for line in open("comtypes/__init__.py"):
+        if line.startswith("__version__ = "):
+            var, value = line.split('=')
+            return value.strip().strip('"').strip("'")
+    raise NotImplementedError("__version__ is not found in __init__.py")
+
+# prepare the same package that is usually uploaded to PyPI
+subprocess.check_output([sys.executable, 'setup.py', 'sdist', '--format=zip'])
+
+filename_for_upload = 'comtypes-{}.zip'.format(read_version())
+target_package = os.path.join(os.getcwd(), 'sdist', filename_for_upload)
+
+# run "pip install comtypes-x.y.z.zip"
+pip_exe = os.path.join(os.path.dirname(sys.executable), 'Scripts', 'pip.exe')
+subprocess.check_output([pip_exe, 'install', target_package])