[3.6] bpo-30495: IDLE: improve textview with docstrings, PEP8 names, more tests. (GH-2283) (#2496)

Split TextViewer class into ViewWindow, ViewFrame, and TextFrame classes so that instances
of the latter two can be placed with other widgets within a multiframe window.
Patch by Cheryl Sabella.
(cherry picked from commit 42bc8be)
diff --git a/Lib/idlelib/pyshell.py b/Lib/idlelib/pyshell.py
index 5b0e5b2..be7bd3d 100755
--- a/Lib/idlelib/pyshell.py
+++ b/Lib/idlelib/pyshell.py
@@ -892,7 +892,7 @@
         try:
             # page help() text to shell.
             import pydoc # import must be done here to capture i/o rebinding.
-            # XXX KBK 27Dec07 use TextViewer someday, but must work w/o subproc
+            # XXX KBK 27Dec07 use text viewer someday, but must work w/o subproc
             pydoc.pager = pydoc.plainpager
         except:
             sys.stderr = sys.__stderr__