ltmain.in: Handle trailing slashes on install commands

ltmain.in: Handle trailing slashes on install commands

A command like:

libtool --mode=install /usr/bin/install -c gck-roots-store-standalone.la
'/image/usr/lib/gnome-keyring/standalone/'

where the path ends with a trailing slash currently fails. This occurs in
software like gnome-keyring or pulseaudio and is because the comparision
code doesn't see the paths as equal. Strip both paths to ensure this works
reliably.

* build-aux/ltmain.in: Strip trailing slashes on install commands.
* NEWS: Update.