Compatibility with conda-build=3

[pelson]

#93 added conda-build 3 API compatibility, but did not add support for actually building recipes that use the features of conda-build 3.

This is a meta-issue for items that crop up:

• AssertionError: modifying metadata after finalization (sorry, don't have the traceback to hand, but it comes from resolved_distribution getattr (line 45).
• Computed binary filename from conda-build-all is different to what conda-build reports. This is because of the hash that gets generated is missing in conda-build-all.

Fixing these things is a pretty deep exercise, and if this is going to get fixed, conda-build-all will cease support for conda-build <3.

[kalefranz]

I ran into a single conda-build 3 related test failure in #96.

https://travis-ci.org/conda-tools/conda-build-all/jobs/341129488

======================================================================
FAIL: test_py_xx_version (conda_build_all.tests.unit.test_resolved_distribution.Test_BakedDistribution_resolve_all)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/conda/lib/python3.5/site-packages/conda_build_all-1.1.4.dev6+head.detached.at.fetch.head-py3.5.egg/conda_build_all/tests/unit/test_resolved_distribution.py", line 69, in test_py_xx_version
    self.assertEqual(ids, ['np18py27_0', 'np18py35_0'])
AssertionError: Lists differ: ['npxxpy>=27_0', 'npxxpy>=27_0'] != ['np18py27_0', 'np18py35_0']
First differing element 0:
'npxxpy>=27_0'
'np18py27_0'
- ['npxxpy>=27_0', 'npxxpy>=27_0']
+ ['np18py27_0', 'np18py35_0']