When using debugger together with numbered bookmarks, it uses the icons of numbered bookmarks
instead of his own.
"This plugin uses hard coded integer marker numbers. This can clash
with other plugins use of markers. Should test for markers with
SC_MARK_AVAILABLE before defining a mark and reset markers used to
SC_MARK_AVAILABLE when cleaning up. Must handle markers not being a
contiguous sequence and none available" (Lex Trotman in editors.geany.general)