Fixes https://github.com/mate-desktop/atril/issues/341

    When annotating or filling a form in a document, this must be saved
    as a different document as atril does not overwrite documents.
    The user can expect to store the modified file in the same place
    than the original document, except when the document lives in
    a temporary directory (e.g. downloaded automatically with a web
    browser), in whose case it must fallback to the Documents
    directory (if set) or the the home directory.

    Previously, atril assumed the latest directory used, or the place
    where an image or attachment was stored last. Such behaviour is
    confusing because the latest place opened might have no relation
    with the document modified.

    Fixes https://bugzilla.gnome.org/show_bug.cgi?id=767611
    Adapted from https://gitlab.gnome.org/GNOME/evince/commit/319a6d49

Use g_debug instead of g_printerr for debug warnings that happen
during normal operation. This way messages are suppressed, unless
the G_MESSAGES_DEBUG variable is set, and we avoid filling everyone's
journal with repetitive debugging info.

https://bugzilla.gnome.org/show_bug.cgi?id=723972

origin commit:
https://gitlab.gnome.org/GNOME/evince/commit/707725e

fixes https://github.com/mate-desktop/atril/issues/315

Make sure not to move the caret in the wrong direction when restoring
the visual line X offset, in case the visual and logical order is
slightly different.

The algorithm used to move the cursor on the next line and restore the
X position across lines works as follows:

1. Move `cursor_offset` to the next line by incrementing it until
   reaching a line break;
2. Find the Y coordinate corresponding to the new cursor_offset;
3. Find the text closest to the new Y coordinate and the previous X
   coordinate.
4. Move cursor_offset to the text at this new (X, Y) location.

The issue lies in step 3, which can find a position on a different line
than expected in case several lines have a nearly the same Y position.

Evince references:
* https://gitlab.gnome.org/GNOME/evince/issues/889
* https://gitlab.gnome.org/GNOME/evince/merge_requests/81
* https://gitlab.gnome.org/GNOME/evince/commit/dddd98b4c7922e2906bba6a31afa07837ae6c39c