win32/uniregistrygen.cc: Open keys with READ if we can't READ/WRITE.

Windows Vista tries to trip us up again, by giving us permission denied
to open HKEY_LOCAL_MACHINE/Software (and probably other keys) with
KEYS_READ | KEYS_WRITE permissions.  But, it works with KEYS_READ.

Rework the iterative subkey opening strategy to try
KEYS_READ | KEYS_WRITE, and fall back to KEYS_READ if this fails.

win32/uniregistrygen.cc

@@ -11,6 +11,15 @@
 WV_LINK(UniRegistryGen);
 
 
+static LONG openregkey(HKEY hLastKey, WvStringParm subkey,
+		       REGSAM samDesired, HKEY *phNextKey, bool create)
+{
+    if (create)
+	return RegCreateKeyEx(hLastKey, subkey, 0, NULL, 0, samDesired, 
+	    NULL, phNextKey, NULL);
+    return RegOpenKeyEx(hLastKey, subkey, 0, samDesired, phNextKey);
+}
+
 // returns a handle to the key specified by key, or, if key specifies a value,
 // a handle to the key containing that value (and setting isValue = true)
 static HKEY follow_path(HKEY from, const UniConfKey &key,
@@ -27,16 +36,15 @@ static HKEY follow_path(HKEY from, const UniConfKey &key,
     {
 	WvString subkey = key.segment(i).printable();
 	HKEY hNextKey;
-
-	if (create)
-	{
-	    result = RegCreateKeyEx(hLastKey, subkey, 0, NULL, 0, samDesired, 
-		NULL, &hNextKey, NULL);
-	}
-	else
-	{
-	    result = RegOpenKeyEx(hLastKey, subkey, 0, samDesired, &hNextKey);
-	}
+
+	result = openregkey(hLastKey, subkey, samDesired, &hNextKey, create);
+	// In Windows Vista, you can't seemingly get KEY_WRITE permissions on
+	// HKEY_LOCAL_MACHINE/Software (and likely others) if running from
+	// within certain processes (presumably ones that set some magic
+	// incantation).  We don't care, of course, since we don't intend to
+	// write this key, and this wonderful fix fixes all.
+	if (result == ERROR_ACCESS_DENIED)
+	    result = openregkey(hLastKey, subkey, KEY_READ, &hNextKey, create);
 
 	if ((result == ERROR_FILE_NOT_FOUND) && (i == n-1))
 	{