Exclude /usr/local from being detected as "Distribution Qt"

/usr/local is the canonical place to put self built applications and
libraries so it should be exlucded from the logic to detect distribution
shipped Qt.

shared/shared.cpp

@@ -810,7 +810,7 @@ DeploymentInfo deployQtLibraries(const QString &appDirPath, const QStringList &a
        setenv("LD_LIBRARY_PATH",newPath.toUtf8().constData(),1);
    }
 
-   if(qtLibsPath.startsWith("/usr/")){
+   if(qtLibsPath.startsWith("/usr/") && !qtLibsPath.startsWith("/usr/local")){
        LogError() << "Bundling Qt provided by distributions is not yet supported by this tool.";
        LogError() << "Please see https://github.com/probonopd/linuxdeployqt/issues/79 and";
        LogError() << "submit a Pull Request to implement this.";