--request-target: instead of --strip-path-slash

... and CURLOPT_REQUEST_TARGET instead of CURLOPT_STRIP_PATH_SLASH.

This option instead provides the full "alternative" target to use in the
request, instead of extracting the path from the URL.

Test 1298 and 1299 updated accordingly.

Idea-by: Evert Pot
Suggestion: https://daniel.haxx.se/blog/2017/06/19/options-with-curl/comment-page-1/#comment-18373

Closes #1593

lib/http.c

@@ -2269,8 +2269,8 @@ CURLcode Curl_http(struct connectdata *conn, bool *done)
   if(result)
     return result;
 
-  if(data->set.strip_path_slash)
-    ppath++;
+  if(data->set.str[STRING_TARGET])
+    ppath = data->set.str[STRING_TARGET];
 
   /* url */
   if(paste_ftp_userpwd)

lib/url.c

@@ -829,9 +829,9 @@ CURLcode Curl_setopt(struct Curl_easy *data, CURLoption option,
          then this can be changed to HEAD later on) */
       data->set.httpreq = HTTPREQ_GET;
     break;
-  case CURLOPT_STRIP_PATH_SLASH:
-    arg = va_arg(param, long);
-    data->set.strip_path_slash = (bool)arg;
+  case CURLOPT_REQUEST_TARGET:
+    result = setstropt(&data->set.str[STRING_TARGET],
+                       va_arg(param, char *));
     break;
   case CURLOPT_FILETIME:
     /*

lib/urldata.h

@@ -1588,7 +1588,7 @@ enum dupstring {
 #ifdef USE_UNIX_SOCKETS
   STRING_UNIX_SOCKET_PATH,      /* path to Unix socket, if used */
 #endif
-
+  STRING_TARGET,                /* CURLOPT_REQUEST_TARGET */
   /* -- end of zero-terminated strings -- */
 
   STRING_LASTZEROTERMINATED,