Improve _test_get_unique_constraints()

Call eq_() in a loop instead of comparing two lists
directly. This makes it much easier to find out which
element is not equal to the reference value.
Fix unique constraints reflection in SQLite

If SQLite keywords are used as column names, they are
quoted. The code parsing the information about table
unique constraints should be modified so that it properly
removes double-quotes from column names.
Fix unique constraints reflection in PostgreSQL

Reflection of unique constraints must preserve the order of columns.
Merge pull request #11 from malor/fix_uc_reflection

Fix unique constraints reflection in SQLite and PostgreSQL