Log Message:
Update to 2.12.18.
Changes from 2.12.17 (properly part of the previous update) included
for reference.

Version 2.12.18 [2008 Sep 8  International Literacy Day]
Bug Fixes

    * Improve security of temporary-file handling.

    * Fix SourceForge bug #1985862 ... SVG output had axis linewidth
      equal to curve line width.

Version 2.12.17 [2008 May 29  Oak Apple Day (England)]
New Features

    * Add GNU readline support so that interactive mode will have
      history, command editing, etc.

Bug Fixes

    * Fix SourceForge bug #1913577 ... superscripts did not end
      correctly, if preceeded by an inline `{}' block.

    * Fix SourceForge bug #1761562 ... y axis name printed upside
      down, for log axes in which user specified a high values at the
      bottom end of the axis