no choice of target directory -- default file permissions outside user directory tend to be ill-defined for Cygwin;

--- a/Admin/Windows/Installer/sfx.txt	Fri Feb 01 21:58:13 2013 +0100
+++ b/Admin/Windows/Installer/sfx.txt	Fri Feb 01 22:24:27 2013 +0100
@@ -1,9 +1,7 @@
 ;!@Install@!UTF-8!
 GUIFlags="64"
 InstallPath="%UserDesktop%"
-BeginPrompt="Unpack Isabelle2013?"
-ExtractPathText="Target directory"
-ExtractTitle="Unpacking Isabelle2013 ..."
+ExtractTitle="Unpacking %%T\Isabelle2013 ..."
 Shortcut="Du,{%%T\Isabelle2013\Isabelle2013.exe},{},{},{},{Isabelle2013},{%%T\Isabelle2013}"
 RunProgram="\"%%T\Isabelle2013\contrib\cygwin\isabelle\init.bat\""
 ;!@InstallEnd@!