Correct PalasoUIWindowsForms.Tests.csproj to have 2-space tabs

Visual Studio generates this file with 2-space tabs, so that is
what we need to have in the repo.  Additionally, before this
change, the indentation was a mix of tabs and spaces.
Add ability to block by acquiring and releasing a unique token
Use a lock file rather than a named mutex

Making named mutexes work in mono requires enabling shared memory
which is not an ideal solution.