Import creates a new trigger instead of updating existing one

Steps to reproduce:
1. Create a host, item and trigger.
2. Set trigger expression so that it contains few empty lines. For example:

{export_host1:export_item1.last()}=0 or

{export_host1:export_item1.last()}=1 or

{export_host1:export_item1.last()}=2

3. Export it any format.
4. Try to import it back again.

Result:
Import creates a new trigger, because of the line endings.

Expected:
It should update the existing trigger.

The problem is that CImportDataNormalizer::normalizeStrings is not recursive.