update ldc to 0.17.0

see https://wiki.ubuntu.com/StableReleaseUpdates for the general strategy:
"Once an Ubuntu release has been completed and published, updates for it are only released under certain circumstances, and must follow a special procedure called a "stable release update" or SRU."

There has to be a specific reason for an update of ldc in Ubuntu 15.10, either important bug fixes or significant improvements compared to the previous version.

Other options: there might be a PPA from somebody who already built an updated package, or a backport of the version for xenial might work on trusty, or you might be able to build this version on your own system yourself.
And xenial will have version 0.17 anyhow. You might consider upgrading to 16.04 as early as possible. You could even do this already now, while this release is still in development status.

Oops, wrong release name, should read "wily" instead of "trusty".

Remember to filter for your release name. You can see this by running:

lsb_release -a

https://launchpad.net/ubuntu/+ppas?name_filter=ldc