add data-dir to InstalledPackageInfo

the datadir location for the inplace InstallDirs was pointing to the top directory
of the package instead of the directory containing the data. this has been fixed.
since templates have already been expanded at this point, datasubdir raises an
exception an cannot be used in generalInstalledPackageInfo. therefore the
full path is stored in datadir.
Merge pull request #2235 from luite/master

add data-dir to InstalledPackageInfo