all: Add flag to keep image data

And use it when converting to a PDF in rsvg-convert.

https://bugzilla.gnome.org/show_bug.cgi?id=721354
Post release version bump
rsvg-convert: Handle gzip compressed input

Code copied from rsvg-view.

https://bugzilla.gnome.org/show_bug.cgi?id=735836
Post release version bump
rsvg-convert: Fix argument processing

Fixes a typo introduced in commit 07e79f07ef789a9bc0b9fb94c41f2af211570889.

https://bugzilla.gnome.org/show_bug.cgi?id=735836
handle: Call close() after write() even on write error

Otherwise the internal xmlDoc will leak.

https://bugzilla.gnome.org/show_bug.cgi?id=736825