Solution file (.sln) lost CRM Developer Toolkit Instance

I’ve encountered this issue several times (especially when we are check in to TFS), that the solution file is not merged properly, and for some reason the developer toolkit bind is removed.

To fix this, edit .sln file using notepad/any text editor, then add:
GlobalSection(CRMSolutionProperties) = preSolution
  SolutionIsBoundToCRM = True
In Global, after:
GlobalSection(TeamFoundationVersionControl) = preSolution