2.1.4 migration fixes: double quotes and drop index

[krilbe]

Fixed two migration bugs:

• Issue #47: Duplicate citation of table name in FbHistoryRepository.ExistsSql.
• Wrong DDL for DROP INDEX.

Based on 2.1.4 branch, but seems to be alright to merge into 2.2.

[krilbe]

We've tested both fixes i our project and use them in production code.

[AppVeyorBot]

:x: Build EntityFrameworkCore.FirebirdSQL 2.1.0.162 failed (commit https://github.com/ralmsdeveloper/EntityFrameworkCore.FirebirdSQL/commit/20a6638431 by @)

[AppVeyorBot]

:x: Build EntityFrameworkCore.FirebirdSQL 2.1.0.162 failed (commit https://github.com/ralmsdeveloper/EntityFrameworkCore.FirebirdSQL/commit/20a6638431 by @)

[krilbe]

Can't seem to get the test suite to run in my devenv, but we do use the fixes in production code and have experiences zero problems.

[ralmsdeveloper]

Thank you very much for trying to help us .. I'm going with a little time, I need more people like you.

[ralmsdeveloper]

I'll use your code and look what happened.

[AppVeyorBot]

:x: Build EntityFrameworkCore.FirebirdSQL 2.1.0.163 failed (commit https://github.com/ralmsdeveloper/EntityFrameworkCore.FirebirdSQL/commit/f7505cf318 by @)

[AppVeyorBot]

:x: Build EntityFrameworkCore.FirebirdSQL 2.1.0.163 failed (commit https://github.com/ralmsdeveloper/EntityFrameworkCore.FirebirdSQL/commit/f7505cf318 by @)

[krilbe]

I added a commit to my branch to fix the DROP INDEX sql in another place. Apparently script generation and direct application in DB uses two different methods for DROP INDEX. This fix is for the latter case.

[ralmsdeveloper]

Thanks @krilbe merge via @https://github.com/ralmsdeveloper/EntityFrameworkCore.FirebirdSQL/commit/125c578085e33dfd9498a0d7a7a9ada3fe3dd23c

I needed to analyze locally, I'll be adding the credits for you!

[ralmsdeveloper]

I will do some work on the provider, so I will be making the necessary adjustments.