Installed files are timestamped with installation time rather than source time

Files installed by the installer framework are timestamped with the time of installation. Files installed by other frameworks (at least installshield and nsis) timestamp installed files with the timestamps of the source files.

Using the source timestamps makes is it easier to see the real age of the installed files, makes the installed directory tree identical on all installations regardless of when the installations were performed, and makes it easier for testers to compare the installed trees on different machines or when installing different sets of components.