Language on send and edit buttons can't be changed in messageselect.php

The text on send and edit buttons of /user/messageselect.php can't be changed.

Patch proposed: substitute lines 78-84 of /user/messageselect.php by the following (in order to take texts from lang strings files)

$strsend = get_string('send');
$stredit = get_string('edit');
echo '<form method="post" action="messageselect.php" style="margin: 0 20px;">
<input type="hidden" name="returnto" value="'.stripslashes($returnto).'">
<input type="hidden" name="id" value="'.$id.'">
<input type="hidden" name="format" value="'.$format.'">
';
echo "<h3>".get_string('previewhtml')."</h3><div class=\"messagepreview\">\n".format_text(stripslashes($messagebody),$format)."\n</div>";
echo "\n<p align=\"center\"><input type=\"submit\" name=\"send\" value=\"$strsend\" /> <input type=\"submit\" name=\"edit\" value=\"$stredit\" /></p>\n</form>";