rename call methods to transform and postprocess

- The `call` methods for nbconvert transformers has been renamed to
  `transform`.
- The `call` methods of nbconvert post-processsors have been renamed to
  `postprocess`.

  pinging @Carreau and @jdrefer, who probably knows who'd be affected by
  this change...  maybe @damianavila, @jakevdp
replace 'transformer' with 'preprocessor'
fixup minor typos from search/replace
renamed transformer to preprocessors
minor typo
minor bug fix, define 'var' in dialog.js.

The 'cell' variable isn't defined and causes and error in the
console
Merge pull request #4044 from ivanov/transform-not-call

rename call methods to transform and postprocess
Merge pull request #4068 from Zsailer/jsfix

minor bug fix, define 'cell' in dialog.js.
Run python-modernize on our codebase
Fix references to __builtin__ module
Fix local imports in external packages
Run python-modernize on bundled pexpect
Manual fix to bundled pexpect
Update bundled path.py to 4.3
Changes to py3compat
Miscellaneous changes to get IPython running on Python 3.3 without 2to3
Changes to get tests running in Python 3
Various changes to get more tests passing
Fix tab completion tests
Fix nbformat tests