[DBAL-178] Fixed an undescriptive error message and a problem when using custom types and their reverse engineering from the database. Allows Type#getMappedDatabaseTypes() to be implemented in custom types, mapping to vendor database types during reverse engineering.

Fix the repeat calling of getReservedKeywordsClass() that causes a considerable slow down when running lots of migrations.

DDC-451 - GUID support through a specific GUID Type, SQL Server specific implementation all others fallback to Varchar fields, no automatic default value = new guid support yet.

[DBAL-220] Add support for Index flags and implement support for SQL Server CLUSTERED/NONCLUSTERED and MySQL FULLTEXT.

Revert a previous commit, apparently the Type engine has two ways of naming types, and there is one that is case-sensitive.