Add requirements.txt to sdist and allow setup.py to use setuptools if detected in environment

MANIFEST.in

@@ -1,3 +1,4 @@
 include AUTHORS
 include LICENSE
 include README.rst
+include requirements.txt

setup.py

@@ -11,6 +11,9 @@ from distutils.command.sdist import sdist
 from distutils.cmd import Command
 from distutils.sysconfig import get_python_lib, PREFIX
 
+if os.environ.get('VIRTUAL_ENV'):
+    from setuptools import setup
+
 execfile('salt/version.py')
 
 class TestCommand(Command):
@@ -48,6 +51,10 @@ else:
 
 libraries = ['ws2_32'] if sys.platform == 'win32' else []
 
+requirements=''
+with open('requirements.txt') as f:
+    requirements = f.read()
+
 setup(
       name=NAME,
       version=VER,
@@ -108,4 +115,5 @@ setup(
                     ['doc/man/salt.7',
                     ]),
                  ],
+      install_requires=requirements,
      )