title: filename completion in gnuplot does not complete the boundary
body: <p>I am using gnuplot for long time, and one problem that I always feel is it is not closing the <code>"</code> on tab completion of filename. 
  e.g. </p>
  
  <pre><code>gnuplot&gt; p 'fo&lt;Tab&gt; 
  </code></pre>
  
  <p>will give me: </p>
  
  <pre><code>gnuplot&gt; p 'fort.10 &lt;cursor here, see the missing '&gt; 
  </code></pre>
  
  <p>while I would expect to have: </p>
  
  <pre><code>gnuplot&gt; p 'fort.10' &lt;cursor here&gt; 
  </code></pre>
  
  <p>I am using the rpm from fedora, which gives: </p>
  
  <pre><code> show version long 
  
          G N U P L O T 
          Version 4.6 patchlevel 3    last modified 2013-04-12 
          Build System: Linux x86_64 
  
          Copyright (C) 1986-1993, 1998, 2004, 2007-2013 
          Thomas Williams, Colin Kelley and many others 
  
          gnuplot home:     http://www.gnuplot.info 
          faq, bugs, etc:   type "help FAQ" 
          immediate help:   type "help"  (plot window: hit 'h') 
  Compile options: 
  -READLINE  +LIBEDITLINE  +HISTORY   
  -BACKWARDS_COMPATIBILITY  +BINARY_DATA   
  +GD_PNG  +GD_JPEG  +GD_TTF  +GD_GIF  +ANIMATION   
  -USE_CWDRC  +X11  +X11_POLYGON  +MULTIBYTE  +X11_EXTERNAL +USE_MOUSE  +HIDDEN3D_QUADTREE   
  +DATASTRINGS  +HISTOGRAMS  +OBJECTS  +STRINGVARS  +MACROS  +IMAGE  +USER_LINETYPES +STATS 
  
  GNUPLOT_DRIVER_DIR = "/usr/libexec/gnuplot/4.6" 
  GNUPLOT_PS_DIR     = "/usr/share/gnuplot/4.6/PostScript" 
  HELPFILE           = "/usr/share/gnuplot/4.6/gnuplot.gih" 
  </code></pre>
  
  <p><strong>After compiling</strong></p>
  
  <pre><code>-READLINE  +LIBEDITLINE  +HISTORY  
  -BACKWARDS_COMPATIBILITY  +BINARY_DATA  
  +GD_PNG  +GD_JPEG  +GD_TTF  +GD_GIF  +ANIMATION  
  -USE_CWDRC  +X11  +X11_POLYGON  +MULTIBYTE  +X11_EXTERNAL +USE_MOUSE  +HIDDEN3D_QUADTREE  
  +DATASTRINGS  +HISTOGRAMS  +OBJECTS  +STRINGVARS  +MACROS  +IMAGE  +USER_LINETYPES +STATS 
  
  GNUPLOT_DRIVER_DIR = "/usr/libexec/gnuplot/4.6"
  GNUPLOT_PS_DIR     = "/usr/share/gnuplot/4.6/PostScript"
  HELPFILE           = "/usr/share/gnuplot/4.6/gnuplot.gih"
  </code></pre>