[BUGFIX] Set Ext.SSL_SECURE_URL to prevent https issues in IE

Ext.SSL_SECURE_URL is javascript:false by default. But this throws the error
"SEC7111: HTTPS security is compromised by res://ieframe.dll/dnserrordiagoff.htm"
in IE. To prevent this we can use the clear.gif URL which is a valid
URL and doesn't create too much traffic

Resolves: #60886
Releases: master, 6.2
Change-Id: I618815318aab3f39aaca54e92ebec4f3d79827c4
Reviewed-on: http://review.typo3.org/35428
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>