[BUG] incorrect indentation when tangling with org-src-preserve-indentation

[Antti Kaihola <akaihola@gmail.com>]

As pointed out in the documentation, when tangling Python code, it's
important to set org-src-preserve-indentation to a non-nil value.
However, tangling still doesn't seem to work correcly: If the first
line of a source code block is indented, it ends up dedented to the
first column in the resulting .py file.


An example:

--8<----8<----8<----8<-- test.org
-*- org-src-preserve-indentation: t -*-

* Main heading

A bit of introduction

#+begin_src python :tangle yes
class ClassDefinition(IsNotIndented):
    class_variable = 'is correctly indented'
#+end_src

#+begin_src python :tangle yes
    def method_definition(self, is_not_indented_correctly):
        print 'the method body'
        print 'is indented correctly'
#+end_src
--8<----8<----8<----8<-- test.org ends


The resulting file after tangling:

--8<----8<----8<----8<-- test.py

class ClassDefinition(IsNotIndented):
    class_variable = 'is correctly indented'

def method_definition(self, is_not_indented_correctly):
        print 'the method body'
        print 'is indented correctly'
--8<----8<----8<----8<-- test.py ends


Note that the "def method_definition" line should be indented with four spaces.