Log Message:
Updated gnuplot to 5.0.6.

Changes in 5.0.6
================
* NEW command 'set micro' enables encoding-specific char for gprintf %c format
* NEW command 'set datafile missing NaN' treats invalid data as if it were missing
* NEW backport updated svg/domterm terminal from development version
* CHANGE - start/end limits in nested iterations are reevaluated dynamically
* CHANGE - revised adjustment of x2label and plot title when x2tics are present
* CHANGE - mark non-free pdf terminal DEPRECATED (to be removed in release 5.2)
* CHANGE - allow fractional font sizes for gdlib terminals
* CHANGE - do not allow inverted R axis (requires support not backported from 5.1)
* CHANGE - allow pointinterval property in 'with lp' for splot as well as for plot
* CHANGE - "linewidth <lw>" is accepted as a terminal option for \ 
aquaterm, qt, wxt
* CHANGE - spline segments outside xrange are ignored rather than treated as errors
* FIX assignment of x/y dimensions in "binary record=(a,b) ... with image"
* FIX wxt - multithreaded wxt was faulting during resize (mutex lock failure)
* FIX windows - timed pause only worked for intervals < 1 second
* FIX Front/back layering of border+grid lines was not always correct in hidden3d
* FIX "set pm3d depthorder interpolate N,M" memory allocation failure
* FIX aquaterm failed to honor request to disable enhanced text markup
* FIX save and show commands failed to list linecolor for lines with "lt \ 
-1"
* FIX the "missing" data flag is honored by "using ($n)" as \ 
it is for "using n"
* FIX error reporting of line number inside a bracketed clause
* FIX gnuplot_x11: possible fix for sporadic use-after-free error
* FIX initialization of hidden3d structures for splot with dots
* FIX track arrowhead properties in hidden3d mode
* FIX tracking of NaN values from function evaluated during binary data input
* FIX 3D rotation does not clobber hidden/visible status of plots