Revised how context menu of tab control is handled to ensure it never appears until the right clicked tab's contents have been redrawn in the detail pane where necessary. This prevents the problem whereby the detail pane was sometimes cleared while the tab context menu was displayed by right clicking a tab.
This fixes bug #87 (https://sourceforge.net/p/codesnip/bugs/87/). See the comments to the bug report for details of why!
