Fix include/define clash with gnulib's unlink module

* src/options.h: Rename options.unlink to options.unlink_requested
* src/init.c: Replace options unlink member by unlink_requested
* src/http.c: Likewise
* src/ftp.c: Likewise

src/ftp.c

@@ -1463,7 +1463,7 @@ Error in server response, closing control connection.\n"));
       else if (opt.noclobber || opt.always_rest || opt.timestamping || opt.dirstruct
                || opt.output_document || count > 0)
         {
-          if (opt.unlink && file_exists_p (con->target))
+          if (opt.unlink_requested && file_exists_p (con->target))
             {
               if (unlink (con->target) < 0)
                 {

src/http.c

@@ -2486,7 +2486,7 @@ open_output_stream (struct http_stat *hs, int count, FILE **fp)
         }
       else if (ALLOW_CLOBBER || count > 0)
         {
-          if (opt.unlink && file_exists_p (hs->local_file))
+          if (opt.unlink_requested && file_exists_p (hs->local_file))
             {
               if (unlink (hs->local_file) < 0)
                 {

src/init.c

@@ -321,7 +321,7 @@ static const struct {
   { "timestamping",     &opt.timestamping,      cmd_boolean },
   { "tries",            &opt.ntry,              cmd_number_inf },
   { "trustservernames", &opt.trustservernames,  cmd_boolean },
-  { "unlink",           &opt.unlink,            cmd_boolean },
+  { "unlink",           &opt.unlink_requested,  cmd_boolean },
   { "useaskpass" ,      &opt.use_askpass,       cmd_use_askpass },
   { "useproxy",         &opt.use_proxy,         cmd_boolean },
   { "user",             &opt.user,              cmd_string },

src/options.h

@@ -61,7 +61,7 @@ struct options
   bool add_hostdir;             /* Do we add hostname directory? */
   bool protocol_directories;    /* Whether to prepend "http"/"ftp" to dirs. */
   bool noclobber;               /* Disables clobbering of existing data. */
-  bool unlink;                  /* remove file before clobbering */
+  bool unlink_requested;        /* remove file before clobbering */
   char *dir_prefix;             /* The top of directory tree */
   char *lfilename;              /* Log filename */
   char *input_filename;         /* Input filename */