Disable overlay scrolling, fixes #4854

[samdroid-apps]

This commit disables overlay scrollig in Sugar. Although this should
be set in the sugar theme, that is not possible.

Setting the environment variable disables the overlay scrolling for
both Sugar Shell and all sub processes (eg. activities).

Ticket URL: http://bugs.sugarlabs.org/ticket/4854

[quozl]

Typo in commit. s/scrollig/ Reviewed. Not tested. Comment added to ticket:

You say it Fedora 22 which introduced the feature, but was it the Gtk+ version which did it rather than Fedora 22? Can you confirm your patch has no effect on systems with earlier versions of Gtk+?

If you amend your commit, please add something to explain that this change has no effect on earlier versions of whatever.

Also, if you have any references to the support status of the environment variable, they would be appreciated.

[godiard]

@samdroid-apps, Please add LIBOVERLAY_SCROLLBAR=0 too, to make it work in ubuntu.