projectexplorer: fix target buildDirectoryChanged signal

Change-Id: Ie46371cac2d345411247c1d2035ee2d5f3b8c00a
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
ios: correcly update executable path in the ui

changing the build directory did not update the path shown in the
run configuration ui (but the correct one would be used)

Task-number: QTCREATORBUG-11080
Change-Id: I4105cb6ffd21bffe59e9bbbccdf427caf88646d6
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>