wmaker: rewrote the update of _NET_WORKAREA property

As reported by Moritz, the Qt toolkit (and maybe a few other ones) are
using the content of this property, but WindowMaker did not set it properly
so for examples the menus in KDE could fail to display in multi-screen
configuration (probably because the toolkit is using the property to make
sure the menu stays in the visible area).

The original code just assumed it was safe to use the usable area of the
1st screen in the list, but unfortunately it is not that simple.

The new code calculates a rectangle that contains the usable region from
all the screens, so the toolkit gets a more accurate value.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
configure: rewrote the detection for WebP image library

Unfortunately, the detection was broken because the header is using a hack
on the function name to provide compatibility between different versions of
the API, which means the usual link test, which uses a known name of a
symbol, cannot work without also using the header to get the hack applied
on the function's name.

The new detection mechanism now simply check for both header and link at
the same time, so we're probably safe until a Major API change is decided,
in which case we will also have to update WRaster's code anyway.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
configure: add detection for O_NOFOLLOW flag to the open function

As discovered by Douglas Torrance, this flag is not really portable, so
this patch adds a check in the configure script to detect if any known
define could help. If no value works, we fall back to defining it with the
neutral value '0', so the compilation will not fail.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WPrefs: improve texts in the Window Handling panel

Did not update the translations msgid because I think translators may
wish to get it visible so they can bring similar improvements.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WPrefs: moved the list of icon animations into an array

By grouping the information together, it makes the code less prone to
errors and easier to maintain as it links things that are related.

Took opportunity to log a message for the case where an invalid value
was found to ease user's debug.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WPrefs: created an array to store the database values for the Icon Position setting

By having an array, it makes the code simpler in many places, thus easier
to maintain. Took opportunity to include a comment about the trick used to
have a value convenient for use.

It is the opportunity to log an error message to user instead of silently
accepting invalid values.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WPrefs: grouped the choices for Window Resize Display in a single place

By having an array, it makes the code simpler in many places, thus easier
to maintain and to implement new possibilities.

It is the opportunity to log an error message to user instead of silently
accepting invalid values.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WPrefs: grouped the choices for Window Move Display in a single place

By having an array, it makes the code simpler in many places, thus easier
to maintain and to implement new possibilities.

It is the opportunity to log an error message to user instead of silently
accepting invalid values.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WPrefs: add an image to represent the window in the Window Placement frame

The original square box did not look like anything, by using an image that
looks like a small window it is more clear to users what it represents.

The image was drawn as an XPM keeping a style consistent with everything
else; it was then converted to TIFF using ImageMagick:
  convert -depth 8 -compress lzw xpm/smallwindow.xpm tiff/smallwindow.tiff

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
WPrefs: add possibility to configure the size of the aperçu

The Icon preference panel have been rearranged to include a slider which
controls the size of the Aperçu. This slider is also used to turn off the
feature, so the related checkbox have been removed from the Misc preference
panel, because it is more convenient to have the related settings at the
same place.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>