Edited Issue: Differ: Handle MaxLength="MAX" in SSDL [726]

3rd party providers can generate this causing the differ to barf. See http://entityframework.codeplex.com/discussions/403176 for example.

Example stack trace:
System.FormatException: Input string was not in a correct format.
at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)
at System.Convert.ToInt32(String value)
at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.BuildColumnModel(XElement property, String entitySetName, ModelMetadata modelMetadata)
at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.BuildAlterColumnOperation(String table, XElement targetProperty, String targetEntitySetName, ModelMetadata targetModelMetadata, XElement sourceProperty, String sourceEntitySetName, ModelMetadata sourceModelMetadata)
at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.<FindChangedColumns>b__ef(<>f__AnonymousType1d`2 <>h__TransparentIdentifiere5)
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.Diff(XDocument sourceModel, XDocument targetModel, String connectionString)
at System.Data.Entity.Migrations.DbMigrator.IsModelOutOfDate(XDocument model, DbMigration lastMigration)
at System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
at System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration)
at System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update(String targetMigration)
at System.Data.Entity.Migrations.Design.ToolingFacade.UpdateRunner.RunCore()
at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run()
Input string was not in a correct format.