filechooser: Fix misleading documentation for gtk_file_chooser_set_preview_widget()

https://bugzilla.gnome.org/show_bug.cgi?id=701174
Fix gtk_text_iter_forward_to_tag_toggle() for end iter

The function must return TRUE only if there is a tag toggle _after_ the
iter, not _at_ the iter. So for the end iter, the function must always
return FALSE.

Add also unit tests for gtk_text_iter_forward_to_tag_toggle().

https://bugzilla.gnome.org/show_bug.cgi?id=691266
GtkFileChooser: Missing hour on today's files for it&hu locales on Win32

The file chooser does not show the hours for files modified today
when using it & hu locales on Win32.  This is due to the %k format conversion
for strftime() that is in Olson's Timezone Package, which msvcrt.dll doesn't have.
Cygwin has it, though.

So for now, we just use a %H format.  While %k would render
six-in-the-morning as " 6" (6 preceded by a space), %H will render it
as "06".

https://bugzilla.gnome.org/show_bug.cgi?id=560337
treeview: Remove duplicate function
filechooser: Actually return a value
testsuite: Don't use deprecated functions
GtkEntry: ellipsize placeholder text

The placeholder string is truncated when there's no
room for it in entry's width.

So, by ellipsizing it, the user can notice the text
was truncated so that they can workaround that by,
for example, maximizing the window.

https://bugzilla.gnome.org/show_bug.cgi?id=702763
Remove rest of gtk-show-input-method-menu and gtk-show-unicode-menu

They are no longer used.
filechooser: In testfilechooser, be strict about the --action option

It would default to GTK_FILE_CHOOSER_ACTION_OPEN if the user's specified --action could not be
parsed.  I can never remember what the right options are, so make the program bail out
if the user specifies an unrecognized option.

Signed-off-by: Federico Mena Quintero <federico@gnome.org>
a11y: Include testdata in EXTRA_DIST

Otherwise tests don't work from a tarball release.