Ensure geos_* funcs imported properly

Use linestring.geos_linestring_from_py in multilinestring instead of importing
as 'from shapely.geometry.linestring import geos_linestring_from_py' as the
speedups won't apply.

Apply the same pattern to MultiPoint and MultiPolygon even though they're
unaffected.
Merge pull request #154 from jwass/speedups_import_fix

Ensure geos_* funcs imported properly