Changed code so that it will be compatible with c++.

1. Added #ifdef extern "C" to public header files.
2. Changed variables that are key words in c++, to different names (like ns instead of namespace).
3. Changed char* to const char* for constant strings.

lib/clixon/clixon_string.h

@@ -78,7 +78,7 @@ static inline char * strdup4(char *str)
     char *dup;
     int len;
     len = align4(strlen(str)+1);
-    if ((dup = malloc(len)) == NULL)
+    if ((dup = (char*) malloc(len)) == NULL)
 	return NULL;
     strncpy(dup, str, len);
     return dup;