Impove opera blank drag image workaround (stolen from codemirror)
Fix issue with blinking cursor on drag over

This happens when dragging from another app. Editor can get focused on app icon hovering (on a Windows taskbar).
[IME] pressing enter on ie reverts last input
use `text-indent: -1em;` to hide cursor on ie

as suggested in https://github.com/ajaxorg/ace/issues/1640
restore textInput.setReadOnly call

needed for disabling contextmenu items
fix spellcheck extension on chrome
fix #1650 Editor looses focus on scrollbar click in the Google Chrome
Merge pull request #1658 from ajaxorg/bugfix/textinput

Bugfix/textinput
multiline strings throw out error line numbers

e.g:

```
<?php
$foo = "test
multiline

string"
a
?>
```
shows  error on line 3 instead of 6.
remove unnecessary new line repace
Change mouse capture target container -> content

To prevent hover activity of scrollbars in Firefox
Merge pull request #1661 from danyaPostfactum/dnd-fixes

Some drag'n'drop fixes
Merge pull request #1660 from adamjimenez/patch-21

multiline strings throw out error line numbers
Fix Webkit context menu on second click
use scroller instead of content

because other widgets inheriting from ace do not have renderer.content
perge pull #1662