Add submodule to sys.path when loading child idl file.

[cocolato]

Fixes: #215

I'm not sure if it's suitable to add the module directly to sys.path, maybe is should implement like this:

for module in thrift.__thrift_meta__["includes"]:
    if module not in sys.modules:
        sys.modules[module.__name__+"_thrift"] = module

then use the import hook to make sure pickle will import the suitable module.

[cocolato]

Now has been updated to a recursive implementation.

[aisk]

I have some concern about whether this code can handle circle including IDLs. Can you add a test case to ensure this?

[cocolato]

Ok, i'll test this part later.

[cocolato]

I have some concern about whether this code can handle circle including IDLs. Can you add a test case to ensure this?

There are already have tests for dead inclusions.

thriftpy2/tests/test_parser.py

Lines 201 to 204 in 91b28ea

	def test_e_dead_include():
	with pytest.raises(ThriftParserError) as excinfo:
	load('parser-cases/e_dead_include_0.thrift')
	assert 'Dead including' in str(excinfo.value)