Warn when uploading testdata with DOS/Windows newlines.

Fixes #1961.

(cherry picked from commit 0f93b1f)

Author: eldering

webapp/src/Service/ImportProblemService.php

@@ -430,6 +430,13 @@ public function importZippedProblem(
                     }
                 }
 
+                if (str_contains($testInput, "\r")) {
+                    $messages['warning'][] = "Testcase file '$baseFileName.in' contains Windows newlines.";
+                }
+                if (str_contains($testOutput, "\r")) {
+                    $messages['warning'][] = "Testcase file '$baseFileName.ans' contains Windows newlines.";
+                }
+
                 $md5in  = md5($testInput);
                 $md5out = md5($testOutput);