[Telepathy] merge: telepathy-sofiasip

[Merge Monkey]

Merge to:

  telepathy-sofiasip

From:

  /home/smcv/public_html/darcs/tp-sofiasip-058-compat

Changes:

  Simon McVittie <simon.mcvittie at collabora.co.uk>
    Resolve conflict with upstream

  Simon McVittie <simon.mcvittie at collabora.co.uk>
    Switch group mixin API to be compatible with telepathy-glib >= 0.5.7 rather than <= 0.5.7

  Simon McVittie <simon.mcvittie at collabora.co.uk>
    Validate that string parameters aren't empty if they shouldn't be, because from 0.5.8 onwards, telepathy-glib won't do that for us