Update res/values-fr/strings.xml
MessageList: add setting to allow 0 preview lines
Show thread as unread if at least one of the messages of the thread is
unread.

Fixes issue 4759.
Merge pull request #235 from rk4an/patch-1

Update res/values-fr/strings.xml
Fix the span range for the text in front of the message preview
Merge branch 'master' of github.com:k9mail/k-9
Merge pull request #238 from maniac103/thread-unread

Show thread as unread if at least one of the messages of the thread is unread.