Update the type comparison code used for schema autogeneration. Compare

Update the type comparison code used for schema autogeneration. Compare

A major rework of the "type comparison" logic is in place which changes the
entire approach by which column datatypes are compared.  Types are now
compared based on the DDL string generated by the metadata type vs. the
datatype reflected from the database.  This means we compare types based on
what would actually render and additionally if elements of the types change
like string length, those changes are detected as well.  False positives
like those generated between SQLAlchemy Boolean and MySQL TINYINT should
also be resolved.   Thanks very much to Paul Becotte  for lots of hard work
and patience on this one.

Fixes: #605
Closes: #619
Pull-request: https://github.com/sqlalchemy/alembic/pull/619
Pull-request-sha: 1a6a3860881081c3b98fdbfc203f8d3af5f98926

Change-Id: I1ab30f2a30fc567cde56b5b8be5f521ff235b67b