Fixed issues with regular expressions.

1) Normalizing line breaks uselessly replaced `\n` with `\n`.
2) [A-z] matches the range including ``^`[]_\``; corrected to `a-z` and
   updated to include full RFC3986-compliant syntax including `+-.`.
3) Collapsing logic uselessly replaced 1 space with 1 space.

class.phpmailer.php

@@ -713,7 +713,7 @@ protected function edebug($str)
             case 'echo':
             default:
                 //Normalize line breaks
-                $str = preg_replace('/(\r\n|\r|\n)/ms', "\n", $str);
+                $str = preg_replace('/\r\n?/ms', "\n", $str);
                 echo gmdate('Y-m-d H:i:s') . "\t" . str_replace(
                     "\n",
                     "\n                   \t                  ",
@@ -3297,7 +3297,7 @@ public function msgHTML($message, $basedir = '', $advanced = false)
                             $message
                         );
                     }
-                } elseif (substr($url, 0, 4) !== 'cid:' && !preg_match('#^[A-z]+://#', $url)) {
+                } elseif (substr($url, 0, 4) !== 'cid:' && !preg_match('#^[a-z][a-z0-9+.-]*://#i', $url)) {
                     // Do not change urls for absolute images (thanks to corvuscorax)
                     // Do not change urls that are already inline images
                     $filename = basename($url);
@@ -3681,7 +3681,7 @@ public function DKIM_HeaderC($signHeader)
         foreach ($lines as $key => $line) {
             list($heading, $value) = explode(':', $line, 2);
             $heading = strtolower($heading);
-            $value = preg_replace('/\s+/', ' ', $value); // Compress useless spaces
+            $value = preg_replace('/\s{2,}/', ' ', $value); // Compress useless spaces
             $lines[$key] = $heading . ':' . trim($value); // Don't forget to remove WSP around the value
         }
         $signHeader = implode("\r\n", $lines);