Display::create_gl_context may create context with incorrect attributes

The surfacelesscontext created uses a default attribute list which may not match the actual attribute list used to create the egl context associated with the nested display.

This is problematic for qtmir - as it creates a temporary context in an effort to query the underlying eglconfig used for the display and inform Qt about R/G/B/A/Depth/stencil sizes.

If the surfaceless context happens to choose a config that has no alpha, qtmir will inform Qt that there's no alpha (when there actually is) and rendering artifacts can occur.

Fix committed into lp:mir at revision None, scheduled for release in mir, milestone 0.20.0

This bug was fixed in the package mir - 0.20.0+16.04.20160219-0ubuntu1

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mir (0.20.0+16.04.20160219-0ubuntu1) xenial; urgency=medium

  [ Alan Griffiths ]
  * New upstream release 0.20.0 (https://launchpad.net/mir/+milestone/0.20.0)
    - ABI summary: Only servers need rebuilding;
      . mirclient ABI unchanged at 9
      . mirserver ABI bumped to 38
      . mircommon ABI unchanged at 5
      . mirplatform ABI unchanged at 11
      . mirprotobuf ABI unchanged at 3
      . mirplatformgraphics ABI bumped to 8
      . mirclientplatform ABI unchanged at 4
      . mirinputplatform ABI unchanged at 5
    - Enhancements:
      . Allow screencasting to create a virtual output (for Miracast)
      . Separate the protocol version number from the client API version macros.
        They're not meant to be related concepts.
      . Add UBSanitizer to the list of build types.
      . logging: Human readable timestamps in DumbConsoleLogger.
      . examples: AdorningDisplayBufferCompositor::composite() no long ignores
        output boundaries and occlusions.
      . examples: Add -a <app name> option to eglapps.
      . common, client: a more flexible way to probe modules: once we've found
        a good current platform we don't even try to load an older one.
      . Fix build and test run with CMAKE_BUILD_TYPE=ThreadSanitizer (missing
        locks).
      . Add MIR_USE_LD_GOLD build option.
    - Bug fixes:
      . unity-system-compositor crashed with std::runtime_error in
        mir::compositor::CompositingFunctor::wait_until_started() from
        usc::MirScreen::set_screen_power_mode (mir_power_mode_on)
        (LP: #1528384)
      . Phone not usable while a call comes in - followed by "restart"
        (LP: #1532607)
      . ui freezes when simultaneously moving mouse & plug/unplug hdmi
        (LP: #1538632)
      . Mir fails to build on xenial today: android_graphic_buffer_allocator.h
        fatal error: hardware/hardware.h: No such file or directory
        (LP: #1539338)
      . [mali] egl_demo_client_flicker has graphics corruption on android
        (LP: #1517205)
      . [testsfail] Intermittent failure in
        TestClientCursorAPI.cursor_passed_through_nested_server (LP: #1525003)
      . [android] External monitor slows rendering (LP: #1532202)
      . Display::create_gl_context may create context with incorrect attributes
        (LP: #1539268)
      . unity-system-compositor locked up in __libc_do_syscall() (LP: #1543594)
      . NestedServer.client_sees_set_scaling_factor intermittent failure
        (LP: #1537798)
      . [android] External monitor slows rendering - part 2 (LP: #1535894)
      . scene: make sure not to set the swapinterval to 0 when an independent
        stream is created. The default should be 1 (like the stream created as
        part of surface creation).
      . Track the displays plugged state to avoid reporting configurations in
        case they are unplugged (LP #1531503). [Cherrypicked from 0.21]
      . mouse pointer support on emulator is broken (LP: #1517597).
        [Cherrypicked from 0.21]
      . move an android-only test that ended up in tests/unit-tests/graphics.
        (LP: ##154...