sidebar-thumbnails: connect to job finished signal before scheduling the job

taken from https://git.gnome.org/browse/evince/commit/?id=6b0630f8c2abd992d65075152dce5fefd9b51f45
ev-jobs: don't forget to unlock the trylock'ed mutex
ev-jobs: fix indentation a bit
epub backend: more anti-NULL protection for epub_document_set_index_pages
zero-init all signals arrays
va_start should be paired with va_end
removed some code that had no effect
don't leak memory
Add support for external links to EvViewPresentation, close #111
Taken from evince commit: 4f8bc8db98020835d2c4d39c902a296b784cf030
From: Carlos Garcia Campos <carlosgc@gnome.org>
Gnome bug: http://bugzilla.gnome.org/show_bug.cgi?id=628711
Save zoom factor in default settings when sizing mode is free, close #87

Taken from evince commit: 78cc0d30890045101ccf107eb30a21aeff94deb0
From: Carlos Garcia Campos <carlosgc@gnome.org>
Gnome bug: http://bugzilla.gnome.org/show_bug.cgi?id=653383