Check for nil tooltip before attempting to reset font colors.

git-svn-id: svn://svn.wowace.com/wow/libqtip-1-0/mainline/trunk@161 dc3927fc-ae5a-46d4-aaf1-084d04d3b661
Remove errant 3px space on the right edge

When initializing or clearing a tooltip, CellMarginH/2 in extra space
was being added to the right side of the tooltip. There was no purpose
to this space.
Properly support tooltips with mixed horizontal margins

When adding a column, record the horizontal margin used on the column.
Take this horizontal margin into account both when resetting the tooltip
size, and when laying out colspans.

Fixes ticket #34.
Remove restriction on setting margins while the tooltip has lines

SetCellMarginH() and SetCellMarginV() currently throw an error if
they're called while the tooltip has lines. There's no need for this
restriction, because changing the margins does not impact any existing
lines. Lifting this restriction allows for having variable vertical
margins between different lines.
Implement function tooltip:SetColumnLeftMargin(colNum, margin)

SetColumnLeftMargin() adjusts the margin to the left of the column,
updating the position of all columns to the right. It cannot be called
on any column that is part of a colspan.
Support variable margins in tooltip:SetColumnLayout()

Update tooltip:SetColumnLayout() to take margins as well. Invocation
looks like:

    tooltip:SetColumnLayout(4, "LEFT", 2, "RIGHT", 6, "LEFT", "RIGHT")

Each number is the margin for the column immediately to its right.

As with SetColumnLeftMargin(), you can't assign a margin to the first
column, and you can't change the margin on a column that's part of a
colspan.
Add tooltip:SetColumnIgnoresColspanWidth()

SetColumnIgnoresColspanWidth() takes a column and, optionally, a boolean
(defaults to true). If true, the given column is marked as being
"fixed". When a colspan is responsible for increasing the tooltip's
width, it will not expand any fixed columns. Usage looks like:

    tooltip:SetColumnLayout(3, "LEFT", "LEFT", "RIGHT")
    tooltip:SetColumnIgnoresColspanWidth(1)

Fixes ticket #35.