visit_ListComp
more try support
 - use compact scala for comprehension syntax for python list comp.
 - translate seq[:] to seq.clone()
pep8 space fixes
types for a few more bits of the python standard library
toward argument, return type support from docstrings in p2s
re-organize __builtin__ around types, implicits, etc.
  - experiment with separate object namespaces basically failed
minor __builtin__ import tweaks
ignore idea IDE stuff
 - py2s runtime for print
 - a few default args
 - special case `from functools import partial as pf_` for scala's f _
   - tmatch() pattern matches ast nodes
 - translate [...] to immutable.IndexedSeq rather than List
   - clone() returns a Seq; use drop(0) instead
 - prefix imports with py. (KLUDGE)
 - fix raise Exception() handling
 - use batteries.print() rather than java println()
 - add self => at the beginning of class blocks
   - _suite() gets optional prefix arg
 - use ast.get_docstring in _doc(); ast.copy_location too
 - functools.partial idiom: pf_(f) translates to f _
 - replace main(**_initial_caps()) dynamic idiom with _with_caps(main)
   - put caps from python standard library (stdout) before others (open_arg)
   - we really only need an Iterable[String] from open_arg
     - TODO: consider an implicit conversion from File to Iterator[String]
             rather than File extends Iterator[String]
- toward separation of concerns between layers in PyToScala
  - factor class LineSyntax out of class PyToScala
  - fp style (separate IO details, single assignment) for import targets
  - fp style for FunctionDef
- some fp idioms for well-typed None handling (option, option_fold)
- indent docstrings on output
- support --debug CLI arg
- stub out vararg support
 - refactor visit_Print to use _items()
 - in visit_For, use a boolean var rather than !iter.isEmpty in else case
 - option(None) should return [] even though it's mutable
oops... fix _doc() and callers
distinguish imports from python standard library from local imports
 - use :forall: T, U to represent [T, U] type params
 - omit self arg on method defs
 - promote __new__ args to class args
   - a few more fp utils

 - tweak __fileinfo__ spacing
 - fix for without else
 - __fileinfo__ needs to be (more) unique
builtins for %, NotImplementedError, TypeError