Merge pull request matplotlib#3162 from tacaswell/tornado_noreq

BLD : made tornado an optional external package

Author: pelson

setupext.py

@@ -1146,7 +1146,7 @@ def get_install_requires(self):
         return [dateutil]
 
 
-class Tornado(SetupPackage):
+class Tornado(OptionalPackage):
     name = "tornado"
 
     def check(self):
@@ -1160,9 +1160,6 @@ def check(self):
 
         return "using tornado version %s" % tornado.version
 
-    def get_install_requires(self):
-        return ['tornado']
-
 
 class Pyparsing(SetupPackage):
     name = "pyparsing"
@@ -1879,14 +1876,14 @@ def check_requirements(self):
             try:
                 # Try in-process
                 msg = self.callback(self)
-                
+
             except RuntimeError:
                 raise CheckFailed("Could not import: are PyQt4 & PyQt5 both installed?")
-                
+
             except:
                 # Raise any other exceptions
                 raise
-                
+
         else:
             # Multiprocessing OK
             try:
@@ -1897,8 +1894,8 @@ def check_requirements(self):
             finally:
                 # Tidy up multiprocessing
                 p.close()
-                p.join()    
-                
+                p.join()
+
         return msg