Add a description of the property shadow-blur-radius on README file. (Bug 11228)

Ensure that shadow_blur_radius > 1 before call to paint the shadow.
Save the cairo_t before change it, and so can be recovered correctly.

Signed-off-by: Eric Koegel <eric.koegel@gmail.com>
I18n: Update translation zh_CN (96%).

213 translated messages, 7 untranslated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
trivial: avoid a compiler warning
Editing menu items with right click optional (Bug #11031)

"/desktop-icons/right-click-edits-menu" xfconf option has been
added. Setting it to FALSE will disable the right click menu
editor and revert to the previous behavior. The menu can still
be edited with a shift+left click in either case.