Replace SHA-1 library with one that is clearly licensed.

The SHA-1 library that we used until now was taken from RFC 3174.  That
library has no clearly free license statement, only a license on the text
of the RFC.  This commit replaces this library with a modified version of
the code from the Apache Portable Runtime library from apr.apache.org,
which is licensed under the Apache 2.0 license, the same as the rest of
Open vSwitch.

NOTICE

@@ -0,0 +1,15 @@
+This file is included in compliance with the Apache 2.0 license,
+available at http://www.apache.org/licenses/LICENSE-2.0.html
+
+Open vSwitch
+Copyright (c) 2007, 2008, 2009 Nicira Networks.
+
+Apache Portable Runtime
+Copyright 2008 The Apache Software Foundation.
+
+This product includes software developed by
+The Apache Software Foundation (http://www.apache.org/).
+
+Portions of this software were developed at the National Center
+for Supercomputing Applications (NCSA) at the University of
+Illinois at Urbana-Champaign.

lib/cfg.c

@@ -143,22 +143,15 @@ cfg_set_file(const char *file_name)
 static int
 update_cookie(void)
 {
+    struct sha1_ctx context;
     int i;
-    SHA1Context context;
 
-    if (SHA1Reset(&context) != shaSuccess) {
-        return -1;
-    }
+    sha1_init(&context);
     for (i = 0; i < cfg.n; i++) {
-        if (SHA1Input(&context, (uint8_t *)cfg.names[i], 
-                    strlen(cfg.names[i])) != shaSuccess) {
-            return -1;
-        }
-        SHA1Input(&context, (uint8_t *)"\n", 1);
-    }
-    if (SHA1Result(&context, cfg_cookie) != shaSuccess) {
-        return -1;
+        sha1_update(&context, cfg.names[i], strlen(cfg.names[i]));
+        sha1_update(&context, "\n", 1);
     }
+    sha1_final(&context, cfg_cookie);
 
     return 0;
 }

lib/cfg.h

@@ -36,7 +36,7 @@ bool cfg_is_dirty(void);
 
 void cfg_get_all(struct svec *);
 
-#define CFG_COOKIE_LEN SHA1HashSize
+#define CFG_COOKIE_LEN SHA1_DIGEST_SIZE
 int cfg_get_cookie(uint8_t *cookie);
 
 void cfg_buf_put(struct ofpbuf *buffer);