Tests for imports and is_definition.
is_definition/Import issue
clear_caches -> clear_time_caches
star_import_cache refactorings: Make it more readable.
change cache_call_signatures, so that it has a well defined input.
Change time_cache, to also host the star_import_cache.
Remove some other _star_import_cache stuff, and with this, #489 should be fixed.
Merge branch 'dev' of github.com:davidhalter/jedi into dev