Expand on <tab> conflict

[udovicic]

If you set expand abbreviation shortcut to <tab>, you are no longer able to produce tabs in text/code.

[codebrainz]

Sorry I didn't see this issue for some reason, must've missed it in my email. I'll try to investigate a bit soon to see if it's a bug but it might also be a limitation of Geany/GTK+ APIs.