[py3] Include requirements.txt and tests in sdist build

This will help make it easier to build and run tests on py2

#495

MANIFEST.in

@@ -4,3 +4,4 @@ include share/chirp.png
 include share/*.1
 include stock_configs/*
 include COPYING
+include *requirements.txt

requirements.txt

@@ -1,4 +1,4 @@
 six
-PyGObject
+PyGObject;python_version>="3.0"
 pyserial
 future

setup.py

@@ -127,7 +127,7 @@ def default_build():
 
     setup(
         name="chirp",
-        packages=["chirp", "chirp.drivers", "chirp.ui"],
+        packages=["chirp", "chirp.drivers", "chirp.ui", "tests", "tests.unit"],
         version=CHIRP_VERSION,
         scripts=["chirpw", "rpttool"],
         data_files=[('share/applications', desktop_files),