Force the use of at least Python 3

prismedia_upload.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # coding: utf-8
 
 """
@@ -97,6 +97,9 @@ except ImportError:
                   'see https://github.com/ahupp/python-magic\n')
     exit(1)
 
+if sys.version_info[0] < 3:
+    raise Exception("Python 3 or a more recent version is required.")
+
 VERSION = "prismedia v0.7.1"
 
 VALID_PRIVACY_STATUSES = ('public', 'private', 'unlisted')