#824 hsteps: Support for width specification via 'set boxwidth'

[Hiroki Motoyoshi]

This patch modifies the hsteps style so that, when the width is not provided by the third column of input data, it default to the width set by 'set boxwidth'. If boxwidth is not set, the conventional method of determining the width will be applied.

The motivation for this change is that, when certain filters (such as bins or smooth frequency) are used in combination with the hsteps, the third column specifying the width may not be available. In the case of the boxes, the same limitation exists, but the width can be specified using 'set boxwidth' command. I wanted to enable the same behavior for the 'hsteps'.

This patch adds support for both boxwidth relative and boxwidth absolute.

This change does not affect the steps, fsteps, histeps, or fillsteps styles, even though they share the "plot_hsteps()" implementation.

Patch file: "gnuplot_hsteps_boxwidth.patch"

Sample scripts:

• "ex1.gp" tests the behavior of 'hsteps' in combination with 'smooth frequency'.
• "ex2.gp" tests the behavior of 'hsteps' when using 'set boxwidth relative'.
• "ex3.gp" demonstrates how to display the Q2 value in a boxplot using 'candlesticks' with 'hsteps nolink'.