newJMenuItem() should use SHORTCUT_KEY_MASK

newJMenuItem() should use SHORTCUT_KEY_MASK variable defined at the top of this class.
Fix: Exception when decreasing indent.

Fix to prevent an exception when decreasing indents if the length
of the last line of file is less than the indent width.
Fix: "Ctrl+," and "Ctrl+/"

Linux and Windows: If you press "Ctrl+," to invoke the preferences dialog,
the file on editor will be marked as "modified". This behavior fixed.

Linux: If you press "Ctrl+/" to comment the line, the line will be replaced
with a single "/" letter. This behavior fixed.
Fix: Exception if type ESC for close confirmation.

If you type an Escape key if a close econfirmation dialog is prompted
for unsaved file, an exception thrown. This behavior fixed.