Release icewm-2.6.0

Keep track of changes to modal flag.
Optimize raising of modal windows.
Fix a memory leak for dynamic menu's.
Free start menu and windowlist menu on exit.
Fix for browse menu's for root and home in start menu.
Eliminate several memory leaks in icon handling.
Use absolute paths for the Exec definition in desktop files.
Only do a passive grab on buttons which are defined by the ButtonRaiseMask.
Guard against buffer overflow when copying the degrees centigrade symbol.
When a focused window can't raise, or there is no overlapping window,
then there shouldn't be a passive button grab by icewm, in order to
improve menu handling in applications which don't use windows for menu's.
Release the passive button grab from a focused window,
when a button click wouldn't raise it, for improved menu
handling for applications with internal menu's (CSS drawing).
These fix the Debian Bug report with number #989764:
"icewm: Intermittently unable to select menu items in drop-down menus.",
which was reported versus IceWM version 2.1.2 on June 12 on:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=989764.

shasum icewm-2.6.0.tar.lz cf8ff3bcba974b6976f33af35fa655ad893f92c6