invert matchparen colors to avoid confusion with inverted cursors

On terminals with inverted cursors or gvim, one gets confused by the matchparen-highlighting.
In the paren-highlighting the background is lighter than the foreground. On dark colorschemes the cursor usually is lighter than the background, too. This means that if the cursor hits one parenthesis the background inverts to dark and the background of the matching parenthesis gets light. This looks like the cursor jumped to the other parenthesis even though it is still on the first one.

This patch switches foreground and background colors of the matchparen highlighting group.