Hover text for includes flash if document view doesn't have focus

[ksnortum]

I have found a small bug -- more of an annoyance. When you startup Frescobaldi with a source file in the document window that has several includes in it, if you hover the mouse over the includes, it looks like it is trying to create all the include hover text very quickly, then disappears. Once the document window has focus, the behavior disappears.

If you need a document with a lot of include lines, you can use the source files from here. Open the file waltzes-op70-book.ly and hover over the include statements without clicking in the document window.

Originally posted by @ksnortum in #1780 (comment)