merged

--- a/etc/settings	Tue Apr 24 16:06:12 2012 +0200
+++ b/etc/settings	Tue Apr 24 16:09:17 2012 +0200
@@ -144,11 +144,9 @@
     PDF_VIEWER="open -W -n"
     ;;
   *)
-    PDF_VIEWER=xpdf
+    PDF_VIEWER=evince
     ;;
 esac
-#PDF_VIEWER=acroread
-#PDF_VIEWER=evince
 
 
 # Printer spool command for PS files

--- a/src/Pure/System/isabelle_system.scala	Tue Apr 24 16:06:12 2012 +0200
+++ b/src/Pure/System/isabelle_system.scala	Tue Apr 24 16:09:17 2012 +0200
@@ -50,9 +50,14 @@
       val standard_system = new Standard_System
       val settings =
       {
-        val env = Map(System.getenv.toList: _*) +
+        val env0 = Map(System.getenv.toList: _*) +
           ("ISABELLE_JDK_HOME" -> standard_system.this_jdk_home())
 
+        val user_home = System.getProperty("user.home")
+        val env =
+          if (user_home == null || env0.isDefinedAt("HOME")) env0
+          else env0 + ("HOME" -> user_home)
+
         val isabelle_home =
           if (this_isabelle_home != null) this_isabelle_home
           else