Fix string shown for ./installed file if writing it fails.

The version was hardcoded previously. Now the entire string
(version, date) is set in a variable which is used both for the
installation script's try at writing the file and then for echo'ing
to the user if the automated writing fails.
Fix string shown for ./installed file if writing it fails - for CLI.

Same as the 0b665ca commit, only this fixes the CLI installer.
Merge pull request #212 from Freso/fix_string_for_installed_file

Fix string shown for ./installed file if writing it fails.