PATH and other environment variables convolute between sessions

[slymz]

It seems the terminal when opened under subsequent, but concurrent Visual Studio sessions gets environment from the first one that was open.

Reproduction:

1. On cmd, set PATH=c:\foo\bar;%PATH%, run devenv
2. Open Whack Whack on VS, and notice the PATH is as expected.
3. Leave it open.
4. On ANOTHER cmd, set PATH=c:\bar\grill;%PATH%, run devenv
5. Open Whack Whack on that new VS, while the other unrelated VS session is running. And notice the PATH has c:\foo\bar, but not c:\bar\grill.

Note: Issue #6 is talking about a similar symptom (I think). However, typing exit on the terminal of the second devenv does not fix this issue. When the terminal comes back open, it is still using the environment from the first session.

This might be an issue with servicehub. I'll look into it.