[PATCH] The autoscaling of images during volatile data refresh works again

[Dima K. <gn...@di...>]

I'm attaching a patch that fixes another set of issues with refreshing
volatile data: autoscaling of images. To observe the issue being fixed,
start up gnuplot and issue

 load "volatile_image_refresh.gp"

where the given file is the attached test case. This is the blutux.rgb
demo image, but stored inline, rather than as a separate file. The load
will succeed. If you then refresh the plot with 'e', the axis ranges
will get confused.

The attached patch fixes this issue, which is actually a regression from
an earlier bug fix. The earlier bug fix reduced the range of the data
that gnuplot can use by 1e6 for the volatile-refresh case. This was
confusing things, so the attached patch makes this range adjustment for
/all/ data. If we can figure out exactly what this original range
reduction was fixing, maybe a better solution can be found. Comment from
the patch and the code:

 This was a regression, caused by an unrelated bug fix that modified the meaning
 of VERYLARGE in some cases. Relevant comment:

 An earlier bug fix introduced this factor in some narrow circumstances
 (AXIS_INIT2D_REFRESH macro) to get around some overflow issues. However, this
 broke some autoscaling functionality (specifically 2d image autoscaling when
 refreshing volatile data) because the STORE_WITH_LOG_AND_UPDATE_RANGE() macro
 has == comparisons with VERYLARGE. Here, I apply the factor to VERYLARGE always.
 The bug fix in question is in the commit titled

  Date: Sun Mar 23 21:39:26 2008 +0000
  Fix macros AXIS_INIT2D_REFRESH and AXIS_UPDATE2D_REFRESH so that the refresh
  command for volatile data works correctly for log axes (SF 1916494).

 The bug it refers to is http://sourceforge.net/p/gnuplot/bugs/636/

 The comment in that commit was

 if an already VERYLARGE x2 and y2 ranges are
 calculated after zoom-out by mouse, then they would become even larger


Re-enabling the first two commented-out lines in the test case reveals
yet another set of issues. I'll look at those in a bit.

dima