Inconsistent behavior for directional rose

[seisman]

Originally reported in GenericMappingTools/pygmt#4025 (comment).

The issues are:

• Directional roses are plotted at bottom-left (x0/0) by default, but it seems the anchor point is "BL" for a simple rose and "MC" for a fancy rose. So, the behavior is inconsistent.
• The box is not drawn for the simple rose when the position is x0/0
• Setting position to jBL looks good, but the box for the simple rose seems to be a square which doesn't fit the simple rose well.

gmt begin map png
	gmt basemap -R100/110/30/35 -JM10c -Baf
	gmt basemap -Td+w2c -F+pblue
	gmt basemap -Td+w2c+f -F+pred

	gmt basemap -R100/110/30/35 -JM10c -Baf -Xw+2c
	gmt basemap -Tdx0/0+w2c -F+pblue
	gmt basemap -Tdx0/0+w2c+f -F+pred

	gmt basemap -R100/110/30/35 -JM10c -Baf -Xw+2c
	gmt basemap -TdjBL+w2c -F+pblue
	gmt basemap -TdjBL+w2c+f -F+pred
gmt end show

Another issue is the default width. The GMT docs say the default width is 10%, but the following script crashes

gmt begin map png
	gmt basemap -R100/110/30/35 -JM10c -Baf
	gmt basemap -Tdx0/0 -F+pblue
	gmt basemap -Tdx0/0+f -F+pred
gmt end show

The error message is:

basemap [ERROR]: Option -T:  Correct syntax
basemap [ERROR]: 	-T[f|m][x]<x0>/<y0>/<size>[/<info>][:wesnlabels:][+<gint>[/<mint>]]
basemap [ERROR]: Could not decode dx0, return NaN.
basemap [ERROR]: Option -T: Could not parse geographic coordinates dx0 and/or 0
basemap [WARNING]:  not a valid number and may not be decoded properly.
basemap [ERROR]: Option -T:  Size must be positive
basemap [ERROR]: Option -T:  <kind> must be 1, 2, or 3

The default width works well if position is not x0/0. I think it's because when x0/0 is used, GMT fallback to the old GMT syntax, which doesn't have default width set.