BLD/BUG/DOC : made pytz a required dependency

closes matplotlib#3423

Author: tacaswell

INSTALL

@@ -201,6 +201,11 @@ libpng 1.2 (or later)
     <http://www.libpng.org/pub/png/libpng.html>`__). libpng requires
     zlib.
 
+`pytz`
+    Used to manipulate time-zone aware datetimes.
+
+
+
 Optional GUI framework
 ^^^^^^^^^^^^^^^^^^^^^^
 
@@ -247,12 +252,6 @@ Optional dependencies
     freetype 2.3 available, please edit L945 of `setupext.py` to reduce
     `min_version` to 2.3.
 
-`pytz`
-    Required if you want to manipulate datetime objects which are time-zone
-    aware.  An exception will be raised if you try to make time-zone aware
-    plots with out `pytz` installed.  It will become a required dependency
-    in 1.4.1.
-
 
 Required libraries that ship with matplotlib
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

setup.py

@@ -66,6 +66,7 @@
     setupext.Numpy(),
     setupext.Six(),
     setupext.Dateutil(),
+    setupext.Pytz(),
     setupext.Tornado(),
     setupext.Pyparsing(),
     setupext.CXX(),

setupext.py

@@ -984,6 +984,7 @@ def get_extension(self):
         self.add_flags(ext)
         return ext
 
+
 class FT2Font(SetupPackage):
     name = 'ft2font'
 
@@ -1183,6 +1184,22 @@ def get_install_requires(self):
         return ['six>={0}'.format(self.min_version)]
 
 
+class Pytz(SetupPackage):
+    name = "pytz"
+
+    def check(self):
+        try:
+            import pytz
+        except ImportError:
+            return (
+                "pytz was not found.")
+
+        return "using pytz version %s" % pytz.__version__
+
+    def get_install_requires(self):
+        return ['pytz']
+
+
 class Dateutil(SetupPackage):
     name = "dateutil"