Doubled references for schemas combined with oneOf, anyOf, allOf

When combining schema that was previously added to components with oneOf, anyOf, allOf it get referenced with doubled reference.

Example:

from apispec import APISpec
from apispec.utils import OpenAPIVersion


spec = APISpec('test', 'v1', OpenAPIVersion('2.0'))
spec.components.schema(
    'Request', 
    {
        'properties': {
            'bool_field': {
                'type': 'boolean'
            },
            'id': {
                'type': 'integer'
            },
            'name': {
                'type': 'string',
                'description': 'name'
            },
            'list_field': {
                'type': 'array',
                'items': {
                    'type': 'integer'
                }
            }
        }
    }
)
operations = {
    'responses': {},
    'parameters': [
        {
            'in': 'body',
            'required': False,
            'name': 'body',
            'schema': {
                'allOf': [
                    '#/definitions/Request'
                ],
                'example': {
                    'id': 1,
                    'name': 'test',
                    'bool_field': True,
                    'list_field': [
                        1, 2, 3
                    ]
                }
            }
        }
    ]
}
spec.path(path='test', operations={'post': operations})
print(spec.to_dict())

Output:
{'paths': OrderedDict([('test', {'post': {'responses': OrderedDict(), 'parameters': [{'in': 'body', 'required': False, 'name': 'body', 'schema': {'allOf': [{'$ref': '#/definitions/#/definitions/Request'}], 'example': {'id': 1, 'name': 'test', 'bool_field': True, 'list_field': [1, 2, 3]}}}]}})]), 'info': {'title': 'test', 'version': 'v1'}, 'swagger': '2.0', 'definitions': {'Request': {'properties': {'bool_field': {'type': 'boolean'}, 'id': {'type': 'integer'}, 'name': {'type': 'string', 'description': 'name'}, 'list_field': {'type': 'array', 'items': {'type': 'integer'}}}}}}

Start by running the provided APISpec example and tracing how components.schema references are processed when the schema is used through path operations with allOf, oneOf, or anyOf. Done means the generated reference contains a single '#/definitions/' prefix, with a regression test covering the demonstrated output.