Fix importer fixup() of module and from-symbol name.

This makes the import_test pass again.
The index_test have to be adapted to check for the right result.
Fix swallowing up trailing comments in an import block.

Fixes the remaining failing test test_imports_dont_delete_trailing_comments.
Add score and location to the repr() of SymbolIndex.
Fix dictionary order dependence in creating aliases.

This leads to sporadic failures under Python 3 with randomized hash.