pg_basebackup: Fix a couple of recently-introduced bugs.

The server expects the compression level to be between 1 and 9, but
Z_DEFAULT_COMPRESSION is -1, so we must not try to send that value
to the server.

Because pg_basebackup's -R option is implemented on the client side,
it can't be used in combination with a backup target. Error out if
someone tries that, instead of silently ignoring the option.

Both issues were reported by Tushar Ahuja; patch by me.

Discussion: http://postgr.es/m/CA+TgmoaMwgdx8HxBjF8hmbohVvPL_0H5LqNrSq0uU+7BKp_Q2A@mail.gmail.com

Author: robertmhaas

src/bin/pg_basebackup/pg_basebackup.c

@@ -1871,6 +1871,12 @@ BaseBackup(void)
 			exit(1);
 		}
 
+		if (writerecoveryconf)
+		{
+			pg_log_error("recovery configuration cannot be written when a backup target is used");
+			exit(1);
+		}
+
 		AppendPlainCommandOption(&buf, use_new_option_syntax, "TABLESPACE_MAP");
 
 		if ((colon = strchr(backup_target, ':')) == NULL)
@@ -1913,7 +1919,7 @@ BaseBackup(void)
 		}
 		AppendStringCommandOption(&buf, use_new_option_syntax,
 								  "COMPRESSION", compressmethodstr);
-		if (compresslevel != 0)
+		if (compresslevel != 0 && compresslevel != Z_DEFAULT_COMPRESSION)
 			AppendIntegerCommandOption(&buf, use_new_option_syntax,
 									   "COMPRESSION_LEVEL", compresslevel);
 	}