Enforce migration version numbering rules

Frequently, it is useful for a project to employ a specific system for migration version numbering. A useful technique for simplying and encoding this system is with a custom attribute that inherits from MigrationAttribute.

An example is below. This uses a system where the migration version is of the format BBYYYYMMDDHHMM, where BB is a branch, YYYY is year, MM is date, and so on.

/// 

/// Mark all migrations with this INSTEAD of [Migration].
/// 
public class MyCustomMigrationAttribute : FluentMigrator.MigrationAttribute
{
    public MyCustomMigrationAttribute(int branchnumber, int year, int month, int day, int hour, int minute, string author)
       : base(CalculateValue(branchnumber, year, month, day, hour, minute))
   {
       this.Author = author;
   }
   public string Author { get; private set; }
   private static long CalculateValue(int branchnumber, int year, int month, int day, int hour, int minute)
   {
      return branchnumber* 1000000000000L + year * 100000000L + month * 1000000L + day * 10000L + hour * 100L + minute;
   }
}

A migration class that uses this attribute might look like this:

[MyCustomMigration(author: "Scott Stafford", changeRequest: 12, year: 2012, month: 8, day: 7, hour: 14, minute: 01)]
public class TestLcmpMigration : Migration
{
    public override void Down() { /* ... */ }
    public override void Up() { /* ... */ }
}