The attached patch refactors tkinter._fix's main logic into a function called 'fix_environ' which is called unconditionally on import, and adds a function 'unfix_environ' to undo the effects of fix_environ.  fix/unfix_environ are then used in all test files that import tkinter (test___all__, test_tcl, test_tk, test_ttk_guionly, test_ttk_textonly, test_idle) to ensure that the environment is properly set to allow Tcl to load and to suppress regrtest's warning that os.environ has been modified.

Since tkinter._fix is an implementation detail, I assume this change isn't against the 'no new features' policy of all currently open branches, but if this needs to wait until 3.5, that's ok with me.