ProjectFileVisitor: Make faster
ProjectFileVisitor: Make faster

Instead of checking if a file is unique with a O(n) operation per file,
do one pass at the end after sorting. This makes opening qtproject.pro
roughly ~7% faster.

Change-Id: If30bdeb8f72e5b28fb900e8e7a45bddb5f9f7822
Reviewed-by: Daniel Teske <d8a411aec9a206efedb4d45b75fe8d13f1e2b628@digia.com>

AltarBeastiful/qt-creator,farseerri/git_code,amyvmiwei/qt-creator,maui-packages/qt-creator,farseerri/git_code,farseerri/git_code,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,danimo/qt-creator,farseerri/git_code,kuba1/qtcreator,martyone/sailfish-qtcreator,farseerri/git_code,amyvmiwei/qt-creator,xianian/qt-creator,maui-packages/qt-creator,xianian/qt-creator,farseerri/git_code,Distrotech/qtcreator,xianian/qt-creator,danimo/qt-creator,kuba1/qtcreator,kuba1/qtcreator,maui-packages/qt-creator,kuba1/qtcreator,danimo/qt-creator,danimo/qt-creator,xianian/qt-creator,Distrotech/qtcreator,martyone/sailfish-qtcreator,xianian/qt-creator,kuba1/qtcreator,xianian/qt-creator,amyvmiwei/qt-creator,martyone/sailfish-qtcreator,Distrotech/qtcreator,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,danimo/qt-creator,maui-packages/qt-creator,xianian/qt-creator,farseerri/git_code,danimo/qt-creator,maui-packages/qt-creator,martyone/sailfish-qtcreator,Distrotech/qtcreator,xianian/qt-creator,AltarBeastiful/qt-creator,danimo/qt-creator,Distrotech/qtcreator,farseerri/git_code,amyvmiwei/qt-creator,kuba1/qtcreator,Distrotech/qtcreator,kuba1/qtcreator,martyone/sailfish-qtcreator,maui-packages/qt-creator,danimo/qt-creator,kuba1/qtcreator,amyvmiwei/qt-creator,xianian/qt-creator,martyone/sailfish-qtcreator,maui-packages/qt-creator,Distrotech/qtcreator,danimo/qt-creator,amyvmiwei/qt-creator,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,kuba1/qtcreator,amyvmiwei/qt-creator