Pin 3.0.x branch against Mapnik 3.0.x mason package

[springmeyer]

Addresses #143.

Currently failing due to #139

[springmeyer]

@artemp - just pushed a variety of minor build fixes to this branch. Can you take it from here? The next steps here are:

• Get the tests 🍏 on travis. There are currently several python unit tests failing.
• Once green merge this branch into v3.0.x
• Port the fixes to master so we have consistency (might be easiest just to copy the files over, but I'll leave it to you how to port).
• Get master 🍏 on travis

[springmeyer]

Failures are now:

======================================================================
FAIL: python_tests.geometry_io_test.test_handling_valid_geojson_empty_geometries
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/mapnik/python-mapnik/mason_packages/.link/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/home/travis/build/mapnik/python-mapnik/test/python_tests/geometry_io_test.py", line 339, in test_handling_valid_geojson_empty_geometries
    eq_(json.replace(" ",""), out_json)
AssertionError: '{"type":"LineString","coordinates":[]}' != 'null'
======================================================================
FAIL: python_tests.geometry_io_test.test_handling_invalid_geojson_empty_geometries
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/mapnik/python-mapnik/mason_packages/.link/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/home/travis/build/mapnik/python-mapnik/test/python_tests/geometry_io_test.py", line 344, in test_handling_invalid_geojson_empty_geometries
    assert_raises(RuntimeError, mapnik.Geometry.from_geojson, json)
AssertionError: RuntimeError not raised

[artemp]

@springmeyer - the failures above indicate that python-mapnik is being built against wrong mapnik core version but I don't quite see where this need to be fixed.

[springmeyer]

@springmeyer - the failures above indicate that python-mapnik is being built against wrong mapnik core version but I don't quite see where this need to be fixed.

@artemp - keep in mind that this is the 3.0.x branch building against mapnik 3.0.13. Do you still think these failures are expected or are they fixable in the tests for this branch?

[springmeyer]

This is green now. Now building against the mapnik v3.0.15 mason package @artemp created.There were some test changes to pgraster than I could not fix, so I overwrote them and ticketed at #155. Next step:

• merge this
• port relevant changes to master, get it green.

[springmeyer]

port relevant changes to master, get it green.

-> #156