gsdx-ogl: don't declare a sampler variable

Nvidia was complaining on the fxaa shader. In doubt I also replaced it in Asmodean's shader
gsdx-ogl: windows: properly setup context flags

* Use a core profile context
* Only enable the debug context in debug build

Close issue #353
wx: properly overwrite trait creation

The fix move the Pcsx2AppTraits definition from core to common part.
It allows to use it in wxAppWithHelpers::CreateTraits

fix issue #352
Merge pull request #356 from PCSX2/issue-fixes

various bug-tracker fixes