Add min_width and min_height options to the Upload class

(manually implementing outdated PR #636)
diff --git a/system/language/english/upload_lang.php b/system/language/english/upload_lang.php
index 88f9ac3..26a5c54 100644
--- a/system/language/english/upload_lang.php
+++ b/system/language/english/upload_lang.php
@@ -36,7 +36,7 @@
 $lang['upload_no_file_selected'] = 'You did not select a file to upload.';
 $lang['upload_invalid_filetype'] = 'The filetype you are attempting to upload is not allowed.';
 $lang['upload_invalid_filesize'] = 'The file you are attempting to upload is larger than the permitted size.';
-$lang['upload_invalid_dimensions'] = 'The image you are attempting to upload exceeds the maximum height or width.';
+$lang['upload_invalid_dimensions'] = 'The image you are attempting to upload doesn\'t fit into the allowed dimensions.';
 $lang['upload_destination_error'] = 'A problem was encountered while attempting to move the uploaded file to the final destination.';
 $lang['upload_no_filepath'] = 'The upload path does not appear to be valid.';
 $lang['upload_no_file_types'] = 'You have not specified any allowed file types.';