add migration failed if DbContext in sperate project

[cuiliang]

I have a DAL project to hold EntityFramework stuff.
When run dnx . ef migration add changecolumn under DAL project, result will be:

Using context 'ApplicationDbContext'.
System.InvalidOperationException: A type named 'StartupProduction' or 'Startup' could not be found in assembly
'Itemz.DAL'.
   在 Microsoft.AspNet.Hosting.Startup.StartupLoader.FindStartupType(String startupAssemblyName, IList`1 diagno
sticMessages)
   在 Microsoft.AspNet.Hosting.Internal.HostingEngine.EnsureStartup()
   在 Microsoft.AspNet.Hosting.Internal.HostingEngine.EnsureApplicationServices()
   在 Microsoft.AspNet.Hosting.Internal.HostingEngine.get_ApplicationServices()
   在 Microsoft.Data.Entity.Commands.ContextTool.TryCreateContextFromStartup(Type type, String startupAssemblyN
ame)
   在 Microsoft.Data.Entity.Commands.ContextTool.CreateContext(Type type, String startupAssemblyName)
   在 Microsoft.Data.Entity.Commands.MigrationTool.CreateContext(Type type, String startupAssemblyName)
   在 Microsoft.Data.Entity.Commands.MigrationTool.AddMigration(String migrationName, String contextTypeName, S
tring startupAssemblyName, String rootNamespace, String projectDir)
   在 Microsoft.Data.Entity.Commands.Program.<>c__DisplayClass11_0.<AddMigration>b__0()
   在 Microsoft.Data.Entity.Commands.Program.Execute(String startupProject, Func`1 invoke)
   在 Microsoft.Data.Entity.Commands.Program.AddMigration(String name, String context, String startupProject)
   在 Microsoft.Data.Entity.Commands.Program.<>c__DisplayClass9_1.<Main>b__6()
   在 Microsoft.Framework.Runtime.Common.CommandLine.CommandLineApplication.Execute(String[] args)
   在 Microsoft.Data.Entity.Commands.Program.Main(String[] args)
.....

If run dnx . ef migration add changecolumn command under Web project which referenced DAL project, the result will be:
···
System.InvalidOperationException: No DbContext was found. Ensure that you're using the correct assembly and tha
t the type is neither abstract nor generic.
在 Microsoft.Data.Entity.Commands.ContextTool.SelectType(IEnumerable1 types, String name) 在 Microsoft.Data.Entity.Commands.MigrationTool.GetContextType(String name) 在 Microsoft.Data.Entity.Commands.MigrationTool.AddMigration(String migrationName, String contextTypeName, S tring startupAssemblyName, String rootNamespace, String projectDir) 在 Microsoft.Data.Entity.Commands.Program.<>c__DisplayClass11_0.<AddMigration>b__0() 在 Microsoft.Data.Entity.Commands.Program.Execute(String startupProject, Func1 invoke)
在 Microsoft.Data.Entity.Commands.Program.AddMigration(String name, String context, String startupProject)
在 Microsoft.Data.Entity.Commands.Program.<>c__DisplayClass9_1.

b__6()
在 Microsoft.Framework.Runtime.Common.CommandLine.CommandLineApplication.Execute(String[] args)
在 Microsoft.Data.Entity.Commands.Program.Main(String[] args)
···

[rowanmiller]

@bricelam assume this is a dupe of something you already have open, so feel free to close with a link to the issue

[bricelam]

Dupe of #2256 and the higher-level #2294