[libsocialcache] Automatically time out stuck image download requests

This commit adds a default timeout to network requests in the image
downloader, to ensure that stuck requests cannot cause processes
which are waiting on the results to hang.
Merge pull request #44 from chriadam/timeout

[libsocialcache] Automatically time out stuck image download requests
Bump version
[libsocialcache] Fix a bug in duplicate request handling

Previously, we only handled duplicate requests in the case where
the request was currently running.  This commit ensures that we also
handle it properly in the case where the request is still queued.
It also adds some more verbose debugging output.
Merge pull request #45 from chriadam/duprequest

[libsocialcache] Fix a bug in duplicate request handling
Bump version
[libsocialcache] Added unread field to FB notification database
Merge pull request #46 from antseppa/unread

[libsocialcache] Added "unread" field to FB notification database
Bump version
Bump pkgconfig version
WIP VK