Fixed implicit conversion of NULL constant to bool (fix #216)

* make sure letter-key shortcuts have ONLY the control key pressed (fixes bug for AltGr->Ctrl+Alt on windows)

Shutdown() test for g.IO.Fonts not being NULL to allow workarounds in case of using multiple contexts #207

Added style.ScrollbarRounding #212

Merge remote-tracking branch 'origin' into 2015-05-menus

Assert on modifiers stack size mismatch between Begni()/End() pairs #204 ...

Experimenting with this. It's helpful but not happy with the idea of
ImGui asserting on that sort of user error.

Examples: test for tooltip over popup.

Allow stacking popups, not really useful yet (wip #126)

Added ImGuiSetCond_Appearing to test the hidden->visible transition.

MenuItem() draft for popups, with Selected option (wip #126)

Tweak RenderCheckMark()

Added RenderCheckMark() helper following the font size ...

Pretty ugly, not sure what's the right way to solve that automatically,
better shown as an "icon" so it doesn't have to necessarily look like
the font.

Comments (#209)

Fix "Debug" window stealing focus/popup #208 #209 @thevaber

Removed inline marker #210

Removed style.AutoFitPadding, using style.WindowPadding makes more sense (the default values were already the same).

Autofit cancel out one worth of vertical spacing for correct symmetry (group and tooltip already do that)

Popup auto-border doesn't spread to its childs #197

Popup have borders by default #197 attenuated border alpha in default theme

Plot: overlay label clipped within frame when bigger than frame

Popups, Tooltips: fit within display. Hidden during size calculation. Fixed popups flicker when changing size. ...

Big change, needed reorder of Begin(). May trigger new bugs.

Fix for width of child windows with scrollbar (broken 376a6a5)

Comments, tweaks, metrics window tweak

Tidying up Begin(): using local copy of 'flags' for brevity

Fixed popup resizing (broken 376a6a5)

Renamed Visible->Active internally

InputText: fixed incorrect edit state after text buffer is modified by user through callback #206

Fix window size after collapsing (broken 376a6a5)

Build fix

Tidying up Begin(): separated blocks needed for auto-resize so it can be moved above position calculation later