StraightLineTool: don't add 1 to even-numbered widths

[dsizzle]

Addressed the "straight line" part of #618

For some strange reason the width had 1 added to it if it was an even number? No idea why but it seems to work fine without that.

[humdingerb]

Works worth width set in the straight line tool setup. If you "Use current brush" though you still get the same as described in #618::

"Width" = 1: shows as 1 pixel width/height
"Width" = 2: shows as 3 pixel width/height
"Width" = 3: shows as 3 pixel width/height
"Width" = 4: shows as 5 pixel width/height
"Width" = 5: shows as 5 pixel width/height
"Width" = 6: shows as 7 pixel width/height

The same happens with "Use current brush" for the freehand tool.

[dsizzle]

You need to pull #619 to get the right behavior for the current brush.

this PR only fixes the straight line tool and needs to be merged in concert with #619

[humdingerb]

Oops, sorry, I thought #619 was merged before you created this PR. All works as intended with #619 added.

[dsizzle]

yay, merged. Thanks!