function errorbar_tick(h,w,xtype)
ERRORBAR_TICK Adjust the width of errorbars
ERRORBAR_TICK(H) adjust the width of error bars with handle H. Error bars width is given as a ratio of X axis lenght (1/80).
ERRORBAR_TICK(H,W) adjust the width of error bars with handle H. The input W is given as a ratio of X axis lenght (1/W). The result is independant of the xaxis units. A ratio between 20 and 80 is usually fine.
ERRORBAR_TICK(H,W,'UNITS') adjust the width of error bars with handle H. The input W is given in the units of the curent xaxis.
