do not allow install with old pytest adaptor (fixes #57 via #65)

Author: sseliverstov

allure-pytest/setup.py

@@ -1,5 +1,17 @@
-import os
+import os,sys
 from setuptools import setup
+from pkg_resources import require, DistributionNotFound, VersionConflict
+
+try:
+    require('pytest-allure-adaptor')
+    print("""
+    You have pytest-allure-adaptor installed.
+    You need to remove pytest-allure-adaptor from your site-packages
+    before installing allure-pytest, or conflicts may result.
+    """)
+    sys.exit()
+except (DistributionNotFound, VersionConflict):
+    pass
 
 PACKAGE = "allure-pytest"
 VERSION = "2.0.0b2"