Use "tk windowingsystem" instead of $env(osxaqua)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@32340 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/tcltk/gis.m/gm.tcl

@@ -77,8 +77,8 @@ if {![catch {set env(HOSTTYPE)}]} {
 }
 
 # add for OSX aqua
-if {![catch {set env(osxaqua)}]} {
-    set osxaqua $env(osxaqua)
+if {[tk windowingsystem] == "aqua"} {
+    set osxaqua "1"
 } else {
     set osxaqua "0"
 }