The icon does not match the others because the NuvolaX icon theme seems
to have vanished from the Internet. Ideally all those admin icons could
use a replacement. But that should be a different PR I guess.

In an older version of PHP a file_exists() call would issue a warning
when the file did not exist. This was fixed in later PHP releases. Since
we require PHP 5.3 now, there's no need to supress any error here
anymore. This might even give a minor performance boost.

Add the class .bounce to any element to let it bounce slightly for 2
seconds. This is useful to make the user aware of some element. Can be
combined with #scroll__here when a long list auto scrolls to a certain
item.

many PHPDocs
some unused variables
some dynamically declared variables declared

- restore lang string as well

fixes fix for FS#2853

When page is removed, and diff can be requested between a revision and
current situation. This results in right revision is 0.

Similar case just after creating a page. A diff between the first
version and nothing before, result in left revision is 0.

In these cases a empty dummy revision is placed as selected value in
dropdown. Otherwise user got distracted by the revisions details shown
in select field,  which are not related to the diff below.

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
 * include upstream change
 * added dropdowns