Blender's debug mode only worked on startup:

- G.f's G_DEBUG flag was being erased in blenkernel/intern/blender.c's
  setup_app_data:

G.f= bfd->globalf

// added a line above it to fix this:

if (G.f & G_DEBUG) bfd->globalf |=G_DEBUG;
G.f= bfd->globalf;

BPython:
- debug info now only shown if Blender is started with '-d' option
- added ~/.blender/scripts to modules sys.path
- added two new functions to Blender.sys: basename and splitext
- added doc for Blender.sys, updated other docs

source/blender/python/api2_2x/doc/Sys.py

@@ -0,0 +1,65 @@
+# Blender.sys module
+
+"""
+The Blender.sys submodule.
+
+sys
+===
+
+This module provides a minimal set of helper functions and data.  Its purpose
+is to avoid the need for the standard Python module 'os', in special 'os.path',
+though it is only meant for the simplest cases.
+
+Example::
+
+  import Blender
+
+  filename = ""
+  def f(name): # file selector callback
+    global filename
+    filename = name
+
+  Blender.Window.FileSelector(f)
+
+  if filename:
+    print 'basename:', Blender.sys.basename(filename)
+    print 'dirname:',  Blender.sys.dirname(filename)
+    print 'splitext:', Blender.sys.splitext(filename)
+
+@type sep: char
+@var sep: the platform-specific dir separator for this Blender: '/'
+    everywhere, except on Win systems, that use '\\'. 
+@type dirsep: char
+@var dirsep: same as L{sep}.
+@type progname: string
+@var progname: the Blender executable (argv[0]).
+
+@attention: The module is called sys, not Sys.
+"""
+
+def basename (path):
+  """
+  Get the base name (filename stripped from dir info) of 'path'.
+  @type path: string
+  @param path: a path name
+  @rtype: string
+  @return: the base name
+  """
+
+def dirname (path):
+  """
+  Get the dir name (dir path stripped from filename) of 'path'.
+  @type path: string
+  @param path: a path name
+  @rtype: string
+  @return: the dir name
+  """
+
+def splitext (path):
+  """
+  Split 'path' into (root, ext), where 'ext' is a file extension.
+  @type path: string
+  @param path: a path name
+  @rtype: list with two strings
+  @return: (root, ext)
+  """