#1145 Fix some EnvVars problems, one of them is a show stopper

[Miguel Gimenez]

The EnvVars plugin has some problems:
* When you configure a project to use an envvar set, you get a "Set not found" error (show stopper)
* Once the previous issue is fixed, If you change the set you must close and reopen the project for the change to be effective
* When you edit a set in Preferences, only the changes to the visible set are saved; the rest are lost
* There was a Unicode-related hack in EnvVarsDebugLog() and an unneeded overload with lots of duplicated code
* Set list is not sorted when shown

The attached patch fixes these, and also:
* corrects coding style
* adds const where applicable
* take constant expressions out of the loops
* some code refactoring for clarity
* removed the _T() macro where not needed

The coding style changes (specially tab size) make the patch difficult to review. I have attached a second patch without most the whitespace changes, this is intended for review only.

[bluehazzard]

Ok,
tested on windows and linux,
works fine for me,

Patch applied in r12537

Thank you a lot