SQLite structure population should be more tolerant

[SmileyChris]

In the sqlite backend, _populate_current_structure has some regex which assumes field names are quoted with double quotes.

I've been working with a sqlite db exported from an mdb, and it uses single quotes instead.

Running a delete_column migration destroyed all fields in the table (due to the _rebuild_table method not containing the original fields).

[andrew]

0.7 has a completely rewritten SQLite module that uses Python's built-in introspection rather than regexes; could you try that, please?