- use two-step iterative process to achieve a reasonable preview size
- fixed precision check; we have to check the speculative decreased precision,
  not the current one
- do not include fmscale gap in the width when we don't draw fmscale


git-svn-id: svn://svn.code.sf.net/p/gwyddion/code/trunk/gwyddion@16661 25697fe4-d644-49b8-9d30-be5465f2adf3
- draw mask correctly with realsquare


git-svn-id: svn://svn.code.sf.net/p/gwyddion/code/trunk/gwyddion@16662 25697fe4-d644-49b8-9d30-be5465f2adf3