OSX: attempt to load UI (menubar) from a nib file

If the app is in a bundle, attempt to load the Main nib file specified in
the bundle's Info.plist. If the file can't be loaded, the stub menubar which
only shows the app name is used.
OSX: Fixed object management at window destruction

Keep around pointers to the window delegate and view and release separately
when the window is destroyed. The reason for that is that NSWindow close
does not destroy manually set delegates nor views (the objects might still
be needed elsewhere).
OSX: expose works more like on X11 now

Moved calling of the expose callback to NSView drawRect to match X11.

Change events test to do MakeCurrent in expose event callback, not
before.
GLXW version bump
X11: process events in order

Using (XCheckMaskEvent(...) || XCheckTypedEvent(..., ClientMessage, ...))
will process all other events before handling ClientMessages, possibly
processing the events in a different order than they arrived in.

Use XCheckIfEvent with an always-true predicate to remove events from
the event queue without blocking while holding the X11 global mutex.
X11: Check for XCreateWindow failure

Check if XCreateWindow fails and bail out.
Add character input events

Add a new event type for unicode text input.

Handle text input in glwt_events test and print out the typed characters
in the window title bar.
X11: Character events using X Input Methods (XIM)

Generate character events from key presses.

Create an X Input Method (XIM) in glwtInit and an X Input Context (XIC)
for each window in glwtWindowCreate.

Use Xutf8LookupString to look up characters on KeyPress events.
Win32: Character events (WM_CHAR)

Handle WM_CHAR messages, decode unicode codepoint from UTF-16.
OSX: Character input events

Process [event characters] in keyDown event handler.
OSX: Fix 10.9 deprecation warnings