C++: fix potential deadlock when closing an editor
C++: fix potential deadlock when closing an editor

When the editor is closed, the CppEditorSupport waits for the
highlighting and semantic info futures to finish. These futures might
access the CppEditorSupport through the CppModelManager, causing a
deadlock on the m_editorSupportMutex.

Change-Id: Ifeb3864ed3bc2666d83607ef50d7bfee8f3d118f
Reviewed-by: Eike Ziller <c142da16c73a95a82d35191bcc55b22835617128@digia.com>
Reviewed-by: Nikolai Kosjar <9571db158ca61a0d070db010803474231fa0cbab@digia.com>

darksylinc/qt-creator,amyvmiwei/qt-creator,xianian/qt-creator,darksylinc/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,richardmg/qtcreator,danimo/qt-creator,kuba1/qtcreator,maui-packages/qt-creator,malikcjm/qtcreator,malikcjm/qtcreator,richardmg/qtcreator,amyvmiwei/qt-creator,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,richardmg/qtcreator,darksylinc/qt-creator,kuba1/qtcreator,omniacreator/qtcreator,darksylinc/qt-creator,richardmg/qtcreator,amyvmiwei/qt-creator,darksylinc/qt-creator,martyone/sailfish-qtcreator,maui-packages/qt-creator,Distrotech/qtcreator,omniacreator/qtcreator,colede/qtcreator,colede/qtcreator,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,danimo/qt-creator,kuba1/qtcreator,xianian/qt-creator,colede/qtcreator,martyone/sailfish-qtcreator,AltarBeastiful/qt-creator,maui-packages/qt-creator,Distrotech/qtcreator,Distrotech/qtcreator,richardmg/qtcreator,colede/qtcreator,farseerri/git_code,Distrotech/qtcreator,danimo/qt-creator,maui-packages/qt-creator,colede/qtcreator,AltarBeastiful/qt-creator,farseerri/git_code,xianian/qt-creator,malikcjm/qtcreator,farseerri/git_code,darksylinc/qt-creator,amyvmiwei/qt-creator,danimo/qt-creator,omniacreator/qtcreator,AltarBeastiful/qt-creator,danimo/qt-creator,Distrotech/qtcreator,malikcjm/qtcreator,richardmg/qtcreator,xianian/qt-creator,omniacreator/qtcreator,martyone/sailfish-qtcreator,danimo/qt-creator,Distrotech/qtcreator,kuba1/qtcreator,maui-packages/qt-creator,amyvmiwei/qt-creator,Distrotech/qtcreator,farseerri/git_code,martyone/sailfish-qtcreator,farseerri/git_code,xianian/qt-creator,farseerri/git_code,darksylinc/qt-creator,kuba1/qtcreator,richardmg/qtcreator,amyvmiwei/qt-creator,malikcjm/qtcreator,malikcjm/qtcreator,danimo/qt-creator,xianian/qt-creator,AltarBeastiful/qt-creator,farseerri/git_code,xianian/qt-creator,colede/qtcreator,maui-packages/qt-creator,maui-packages/qt-creator,martyone/sailfish-qtcreator,kuba1/qtcreator,colede/qtcreator,kuba1/qtcreator,omniacreator/qtcreator,omniacreator/qtcreator,danimo/qt-creator,martyone/sailfish-qtcreator,malikcjm/qtcreator,danimo/qt-creator,kuba1/qtcreator,xianian/qt-creator,AltarBeastiful/qt-creator,darksylinc/qt-creator,AltarBeastiful/qt-creator,amyvmiwei/qt-creator,kuba1/qtcreator,omniacreator/qtcreator,xianian/qt-creator,farseerri/git_code