fixed method names in relextract doctests
added 'untagged_filler' to the relextract doctest
made '_tree2semi_rel' public
In ISRI stemmer's norm(), fix erroneous raw-string substitution
ISRI stemmer: Corrections to logic (and many style fixes)

Let me stress up front: I do not speak any Arabic at all. There are a small
number of places where I have fixed some very obviously broken logic, but by
and large I have left the actual work being done by this file alone.

Places where I did change the logic:

* suf32() and pre32(). These both start with "if word is at least 6 letters
  long", and go through the length-three affixes to see if each can be
  removed. The only sensible way for the "if the word is at least 5 letters
  long, go through the length-two affixes" block to work is for it to be at
  the same indentation level, but instead (in both methods) it was indented to
  be inside the length-three affix removal block. I've reindented these.

* pro_w64(). The first check in this method was

     if (self.stm[0] and self.stm[4])=='\u0627':

  This is clearly wrong; the intent is to check whether both the first and
  fifth letters are \u0627, but instead it always fails, because a boolean is
  not equal to a string. I've changed this to be two separate conditions.

The majority of corrections in this commit are:

* pep8 changes - putting spaces around operators, standardizing the spacing of
  inline comments, etc. (I did *not* change the line lengths, though many of
  the lines are quite long, because I wasn't sure what the standard for NLTK
  is.)

* Pythonic changes - having all methods take the stem as an argument and
  return the stem, rather than modifying "self.stm" and also (sometimes, but
  not always) returning self.stm. Changing "if <condition> & <condition>" to
  "if <condition> and <condition>". That sort of thing.

* Assorted other stylistic changes - moving the hard-to-read inline comments
  on the lists in __init__ to appear above each list instead. Correcting the
  spelling of "intial" to "initial" in a variable name. Etc.
Remove 'SVN Revision' from the list of fields that can be displayed in the downloader GUI, since it's not applicable anymore.
Fixed doctest for batch name change
Merge pull request #628 from heatherleaf/develop

Fixed doctest for batch name change
Merge pull request #625 from alexrudnick/develop

Remove 'SVN Revision' from the downloader GUI
Merge pull request #619 from Tahnan/develop

ISRI stemmer: Corrections to logic (and many style fixes)
Merge pull request #617 from jskda/pull_request.relextract

Some fixes to the relextract doctests
Made the backtracking rd-parser use iterators instead of lists
Replaced Chart._choose_children with itertools.product
Made .parses() and .trees() return an iterator
Removed ParserI.prob_parse() and .prob_parse_sents()
Merge branch 'develop' into iter
Merge pull request #634 from heatherleaf/iter

more iterators in parsers