test 1515: add MSYS support by passing a relative path

MSYS would otherwise turn a /-style path into a C:\-style path.

tests/data/test1515

@@ -45,7 +45,7 @@ lib1515
 caching of manual libcurl DNS entries after DNS cache timeout
 </name>
 <command>
-/path/1515 %HOSTIP %HTTPPORT
+path/1515 %HOSTIP %HTTPPORT
 </command>
 </client>
 

tests/libtest/lib1515.c

@@ -130,7 +130,7 @@ int test(char *URL)
 
   for(i = 1; i <= count; i++) {
     char target_url[256];
-    snprintf(target_url, sizeof(target_url), "http://testserver.example.com:%s%s%04d", port, path, i);
+    snprintf(target_url, sizeof(target_url), "http://testserver.example.com:%s/%s%04d", port, path, i);
 
     /* second request must succeed like the first one */
     if((res = do_one_request(multi, target_url, dns_entry)))