Wrap stdout/stderr to avoid "Not enough space" in Python 2 on Windows 7

When you set the standard streams to binary you seem to only be able to
write up to some limit in a single call to write. So we wrap the streams
and write in chunks to avoid this.

A similar hack was also implemented in Python 3 to work around this. But
that hack doesn't seem to exist in Python 2.

This might have unintended side effects due to replacing the standard
stream objects.

Fixes #825

click/_compat.py

@@ -620,6 +620,7 @@ def func():
             return rv
         rv = wrapper_func()
         try:
+            stream = src_func()  # In case wrapper_func() modified the stream
             cache[stream] = rv
         except Exception:
             pass

click/_winconsole.py

@@ -201,6 +201,30 @@ def __repr__(self):
         )
 
 
+class StreamWrapper(object):
+    """
+    Wraps a stream (such as stdout), acting as a transparent proxy for all
+    attribute access apart from method 'write()' which we wrap to write in
+    limited chunks due to a Windows limitation on binary console streams.
+    """
+    def __init__(self, wrapped):
+        # double-underscore everything to prevent clashes with names of
+        # attributes on the wrapped stream object.
+        self.__wrapped = wrapped
+
+    def __getattr__(self, name):
+        return getattr(self.__wrapped, name)
+
+    def write(self, text):
+        total_to_write = len(text)
+        written = 0
+
+        while written < total_to_write:
+            to_write = min(total_to_write - written, MAX_BYTES_WRITTEN)
+            self.__wrapped.write(text[written:written+to_write])
+            written += to_write
+
+
 def _get_text_stdin(buffer_stream):
     text_stream = _NonClosingTextIOWrapper(
         io.BufferedReader(_WindowsConsoleReader(STDIN_HANDLE)),
@@ -209,13 +233,21 @@ def _get_text_stdin(buffer_stream):
 
 
 def _get_text_stdout(buffer_stream):
+    if PY2:
+        buffer_stream = StreamWrapper(buffer_stream)
+        sys.stdout = StreamWrapper(sys.stdout)
+
     text_stream = _NonClosingTextIOWrapper(
         _WindowsConsoleWriter(STDOUT_HANDLE),
         'utf-16-le', 'strict', line_buffering=True)
     return ConsoleStream(text_stream, buffer_stream)
 
 
 def _get_text_stderr(buffer_stream):
+    if PY2:
+        buffer_stream = StreamWrapper(buffer_stream)
+        sys.stderr = StreamWrapper(sys.stderr)
+
     text_stream = _NonClosingTextIOWrapper(
         _WindowsConsoleWriter(STDERR_HANDLE),
         'utf-16-le', 'strict', line_buffering=True)