Major createMigrationTable() performance improvement
minor #75 Major createMigrationTable() performance improvement (dtrethewey)

This PR was squashed before being merged into the 1.0.x-dev branch (closes #75).

Discussion
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Major createMigrationTable() performance improvement

In the createMigrationTable() method in Configuration, the schema is re-created every time the method is called if the migration table already exists.

We were trying to run a fairly large set of migrations across multiple databases and this method is called many times, resulting in lots of createSchema() requests which really slows the migrations down.

Now it's only ever called once per database inside this method greatly improving performance.

Commits
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7ca271b Major createMigrationTable() performance improvement