Move SHA256 class to libroot instead of linking libshared into libroot.

Discussed with PulkoMandy and on the haiku-commits mailing list.

Thanks to @jessicah for compile-testing and fixing 2 small issues I missed.

headers/build/private/libroot/SHA256.h

@@ -0,0 +1 @@
+#include "../../../private/libroot/SHA256.h"

headers/build/private/shared/SHA256.h

@@ -1 +0,0 @@
-#include <../private/shared/SHA256.h>

headers/private/libroot/SHA256.h

@@ -2,8 +2,8 @@
  * Copyright 2008, Ingo Weinhold, ingo_weinhold@gmx.de.
  * Distributed under the terms of the MIT License.
  */
-#ifndef SHA_256_H
-#define SHA_256_H
+#ifndef _SHA_256_H
+#define _SHA_256_H
 
 
 #include <SupportDefs.h>
@@ -11,6 +11,8 @@
 
 #define SHA_DIGEST_LENGTH	32
 
+namespace BPrivate {
+
 
 class SHA256 {
 public:
@@ -36,4 +38,9 @@ private:
 };
 
 
-#endif	// SHA_256_H
+} // namespace BPrivate
+
+using BPrivate::SHA256;
+
+
+#endif	// _SHA_256_H