simplified Cygwin root: warm start via env, cold start via property, no registry magic;

--- a/lib/scripts/getsettings	Thu May 24 22:49:39 2012 +0200
+++ b/lib/scripts/getsettings	Thu May 24 23:13:06 2012 +0200
@@ -23,7 +23,7 @@
 
   CLASSPATH="$(cygpath -i -u -p "$CLASSPATH")"
   function jvmpath() { cygpath -i -C UTF8 -w -p "$@"; }
-  THIS_CYGWIN="$(jvmpath "/")"
+  CYGWIN_ROOT="$(jvmpath "/")"
 else
   if [ -z "$USER_HOME" ]; then
     USER_HOME="$HOME"

--- a/src/Pure/System/cygwin.scala	Thu May 24 22:49:39 2012 +0200
+++ b/src/Pure/System/cygwin.scala	Thu May 24 23:13:06 2012 +0200
@@ -8,7 +8,6 @@
 package isabelle
 
 import java.lang.System
-import java.lang.reflect.Method
 import java.io.File
 import java.net.URL
 import java.awt.Component
@@ -16,73 +15,8 @@
 
 object Cygwin
 {
-  /* registry access */
-
-  // Some black magic involving private WindowsPreferences from Sun, cf.
-  // http://www.docjar.com/html/api/java/util/prefs/WindowsPreferences.java.html
-
-  private val WindowsPreferences = Class.forName("java.util.prefs.WindowsPreferences")
-
-  private val HKEY_CURRENT_USER = 0x80000001
-  private val HKEY_LOCAL_MACHINE = 0x80000002
-  private val KEY_READ = 0x20019
-  private val NATIVE_HANDLE = 0
-  private val ERROR_CODE = 1
-
-  private def C_string(s: String): Array[Byte] =
-    (s + "\0").getBytes("US-ASCII")
-
-  private def J_string(bs: Array[Byte]): String =
-    new String(bs, 0, bs.length - 1, "US-ASCII")
-
-  private val INT = Integer.TYPE
-  private val BYTES = (new Array[Byte](0)).getClass
-
-  private def open_key(handle: Int, subkey: Array[Byte], mask: Int): Array[Int] =
-  {
-    val m = WindowsPreferences.getDeclaredMethod("WindowsRegOpenKey", INT, BYTES, INT)
-    m.setAccessible(true)
-    m.invoke(null, handle.asInstanceOf[Object], subkey.asInstanceOf[Object],
-      mask.asInstanceOf[Object]).asInstanceOf[Array[Int]]
-  }
-
-  private def close_key(handle: Int): Int =
-  {
-    val m = WindowsPreferences.getDeclaredMethod("WindowsRegCloseKey", INT)
-    m.setAccessible(true)
-    m.invoke(null, handle.asInstanceOf[Object]).asInstanceOf[Int]
-  }
-
-  private def query(handle: Int, name: Array[Byte]) =
-  {
-    val m = WindowsPreferences.getDeclaredMethod("WindowsRegQueryValueEx", INT, BYTES)
-    m.setAccessible(true)
-    m.invoke(null, handle.asInstanceOf[Object], name.asInstanceOf[Object]).
-      asInstanceOf[Array[Byte]]
-  }
-
-  def query_registry(sys: Boolean, path: String, name: String): Option[String] =
-  {
-    val handle = if (sys) HKEY_LOCAL_MACHINE else HKEY_CURRENT_USER
-    val result = open_key(handle, C_string(path), KEY_READ)
-    if (result(ERROR_CODE) != 0) None
-    else {
-      val res = query(result(NATIVE_HANDLE), C_string(name))
-      if (res == null) None
-      else Some(J_string(res))
-    }
-  }
-
-  def query_registry(path: String, name: String): Option[String] =
-    query_registry(false, path, name) orElse
-      query_registry(true, path, name)
-
-
   /* Cygwin installation */
 
-  private val CYGWIN_SETUP1 = "Software\\Cygwin\\setup"
-  private val CYGWIN_SETUP2 = "Software\\Wow6432Node\\Cygwin\\setup"
-
   private def sanity_check(root: File)
   {
     if (!new File(root, "bin\\bash.exe").isFile ||
@@ -93,15 +27,12 @@
 
   def check_root(): String =
   {
-    val this_cygwin = System.getenv("THIS_CYGWIN")
-    val cygwin_root = System.getProperty("cygwin.root")
+    val cygwin_root1 = System.getenv("CYGWIN_ROOT")
+    val cygwin_root2 = System.getProperty("cygwin.root")
     val root =
-      if (this_cygwin != null && this_cygwin != "") this_cygwin
-      else if (cygwin_root != null && cygwin_root != "") cygwin_root
-      else
-        query_registry(CYGWIN_SETUP1, "rootdir") orElse
-        query_registry(CYGWIN_SETUP2, "rootdir") getOrElse
-        error("Failed to determine Cygwin installation -- version 1.7.x required")
+      if (cygwin_root1 != null && cygwin_root1 != "") cygwin_root1
+      else if (cygwin_root2 != null && cygwin_root2 != "") cygwin_root2
+      else error("Bad Cygwin installation: unknown root")
     sanity_check(new File(root))
     root
   }