Does not preserve timestamp of symbolic links

[Phil Ruffwind]

It seems that duplicity does not preserve the timestamp (specifically modification time) of symbolic links.

Test case:

1. Create some symbolic links in a directory A (possibly broken links, doesn't matter). Wait a minute or so.
2. duplicity A file://B
3. duplicity file://B C

Expected: same timestamp shown with ls -l as in directory A
Actual: timestamp of symbolic links is the time of restore (step 3) instead

Does not affect normal files, just symbolic links.

duplicity 0.7.12
Python 3.6.1
Linux 4.11.3-1-ARCH