Migrated bug from GitHub: https://github.com/Unity-Technologies/InputSystem/issues/117

I have just tried installing this plugin and am getting 3 errors:

1. /myproject/Packages/com.unity.inputsystem/InputSystem/Controls/InputControlLayout.cs(541,40): error CS0121: The call is ambiguous between the following methods or properties: System.MissingExtensions.GetCustomAttribute<UnityEngine.Experimental.Input.InputControlLayoutAttribute>(this System.Reflection.MemberInfo, bool) and UnityEngine.Experimental.Input.Net35Compatibility.Net35Compatibility.GetCustomAttribute<UnityEngine.Experimental.Input.InputControlLayoutAttribute>(this System.Reflection.MemberInfo, bool)

2. /myproject/Packages/com.unity.inputsystem/InputSystem/Controls/InputControlLayout.cs(742,51): error CS0121: The call is ambiguous between the following methods or properties: System.MissingExtensions.GetCustomAttribute<System.Runtime.CompilerServices.FixedBufferAttribute>(this System.Reflection.MemberInfo, bool) and UnityEngine.Experimental.Input.Net35Compatibility.Net35Compatibility.GetCustomAttribute<System.Runtime.CompilerServices.FixedBufferAttribute>(this System.Reflection.MemberInfo, bool)

3. /myproject/Packages/com.unity.inputsystem/InputSystem/InputManager.cs(244,26): error CS0121: The call is ambiguous between the following methods or properties: System.MissingExtensions.GetCustomAttribute<System.SerializableAttribute>(this System.Reflection.MemberInfo, bool) and UnityEngine.Experimental.Input.Net35Compatibility.Net35Compatibility.GetCustomAttribute<System.SerializableAttribute>(this System.Reflection.MemberInfo, bool)

Steps to reproduce:

1. Downloaded Unity 2018.2b (was using 2017.x until this morning)
2. Opened my project on Unity 2018.2b to update/reimport assets on 2018 format
3. Made a small change to my project and saved it (to make sure it's saved on 2018 format)
4. Copied Packages/com.unity.inputsystem/ folder to the Packages folder in my project
5. Alt-tabbed to Unity and allowed it to process/import
(At this point the 3 errors already showed up on the console, but I proceeded)
6. Changed Active Input Handling to Both
7. Restarted Unity
(The 3 errors showed up again)