Remove dependency on base64c. Use libsodium's. Also consolidate the calls, as the usage is quite special.

git-svn-id: https://www.unprompted.com/svn/projects/tildefriends/trunk@4175 ed5197a5-7fde-0310-b194-c3ffbd925b24

src/tests.c

@@ -623,7 +623,9 @@ static void _test_b64(const tf_test_options_t* options)
 	fprintf(file,
 		"'use strict';\n"
 		"print(base64Encode('hello'));\n"
-		"if (base64Decode(base64Encode('hello')) !== 'hello') {\n"
+		"let x = base64Decode(base64Encode('hello'));\n"
+		"if (x !== 'hello') {\n"
+		"	print(x);\n"
 		"	exit(1);\n"
 		"}\n"
 		);