[meld] Add checking for python version in Setup.py, like meld itself (bgo#772934).

[Kai Willadsen <kaiw src gnome org>]

commit 691cb53327b199e929ef51fe7d2116560146b83f
Author: Vasily Galkin <galkin-vv yandex ru>
Date:   Wed Jan 18 22:34:04 2017 +0300

    Add checking for python version in Setup.py, like meld itself (bgo#772934).
    
    Also setup.py PyPI classifier updated according to 2->3 porting guide.

 bin/meld     |    5 ++---
 meld/conf.py |    1 +
 setup.py     |    6 +++++-
 3 files changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/bin/meld b/bin/meld
index 483b705..21c47d4 100755
--- a/bin/meld
+++ b/bin/meld
@@ -170,7 +170,6 @@ def show_error_and_exit(error_text):
 
 def check_requirements():
 
-    pyver = (3, 3)
     gtk_requirement = (3, 14)
     glib_requirement = (2, 36, 0)
     gtksourceview_requirement = (3, 14, 0)
@@ -182,8 +181,8 @@ def check_requirements():
             modver = mod + " " + ".".join(map(str, ver))
             show_error_and_exit(_("Meld requires %s or higher.") % modver)
 
-    if sys.version_info[:2] < pyver:
-        missing_reqs("Python", pyver)
+    if sys.version_info[:2] < meld.conf.PYTHON_REQUIREMENT_TUPLE:
+        missing_reqs("Python", meld.conf.PYTHON_REQUIREMENT_TUPLE)
 
     # gtk+ and related imports
     try:
diff --git a/meld/conf.py b/meld/conf.py
index 6c8f2cd..2aafdde 100644
--- a/meld/conf.py
+++ b/meld/conf.py
@@ -11,6 +11,7 @@ LOCALEDIR = os.path.join(sys.prefix, "share", "locale")
 # END
 UNINSTALLED = False
 UNINSTALLED_SCHEMA = False
+PYTHON_REQUIREMENT_TUPLE = (3, 3)
 
 # Installed from main script
 _ = lambda x: x
diff --git a/setup.py b/setup.py
index 05f0af6..abb768e 100755
--- a/setup.py
+++ b/setup.py
@@ -2,10 +2,14 @@
 
 from distutils.core import setup
 import glob
+import sys
 
 import meld.build_helpers
 import meld.conf
 
+if sys.version_info[:2] < meld.conf.PYTHON_REQUIREMENT_TUPLE:
+    version = ".".join(map(str, meld.conf.PYTHON_REQUIREMENT_TUPLE))
+    raise Exception("Meld setup requires Python %s or higher." % version)
 
 setup(
     name=meld.conf.__package__,
@@ -22,7 +26,7 @@ setup(
         'Intended Audience :: System Administrators',
         'License :: OSI Approved :: GNU General Public License v2 or later (GPLv2+)',
         'Programming Language :: Python',
-        'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 3 :: Only',
         'Topic :: Desktop Environment :: Gnome',
         'Topic :: Software Development',
         'Topic :: Software Development :: Version Control',