Allowing SQLite3 to correctly build value sets in sets of 500 (the maximum allowed by SQLite3's SQLITE_LIMIT_COMPOUND_SELECT constant).

* Moving the work of parsing import value sets into their own objects to allow specific adapters to choose a different strategy for parsing.

Ref: http://www.sqlite.org/limits.html

[#87]
Merge branch 'issues/87_sqlite'
Merge commit 'cbcdb2b1b78cc395863311d92acfdb31e9cf38b2' into update_from_remote

Conflicts:
	lib/activerecord-import/adapters/abstract_adapter.rb