strerror: improve two URL API error messages

lib/strerror.c

@@ -476,7 +476,7 @@ curl_url_strerror(CURLUcode error)
     return "Port number was not a decimal number between 0 and 65535";
 
   case CURLUE_UNSUPPORTED_SCHEME:
-    return "This libcurl build doesn't support the given URL scheme";
+    return "Unsupported URL scheme";
 
   case CURLUE_URLDECODE:
     return "URL decode error, most likely because of rubbish in the input";
@@ -530,7 +530,7 @@ curl_url_strerror(CURLUcode error)
     return "Bad file:// URL";
 
   case CURLUE_BAD_SLASHES:
-    return "Unsupported number of slashes";
+    return "Unsupported number of slashes following scheme";
 
   case CURLUE_BAD_SCHEME:
     return "Bad scheme";

tests/data/test1538

@@ -160,7 +160,7 @@ u1: An invalid CURLU pointer was passed as argument
 u2: An invalid 'part' argument was passed as argument
 u3: Malformed input to a URL function
 u4: Port number was not a decimal number between 0 and 65535
-u5: This libcurl build doesn't support the given URL scheme
+u5: Unsupported URL scheme
 u6: URL decode error, most likely because of rubbish in the input
 u7: A memory function failed
 u8: Credentials was passed in the URL when prohibited
@@ -183,7 +183,7 @@ u24: Bad password
 u25: Bad path
 u26: Bad query
 u27: Bad scheme
-u28: Unsupported number of slashes
+u28: Unsupported number of slashes following scheme
 u29: Bad user
 u30: CURLUcode unknown
 </stdout>