make all commands (see manual 17.5) entered manually,
with .control section or by script case insensitive.
generally in inpcom.c everything is converted to lowercase,
but there are exceptions, e.g. "wrdata", which might be
followed by arguments whose case needs to be preserved.
(most notably filenames)
Thanks to Mathias Gebhardt, who reported this bug in
#310 Command parser problem with wrdata
http://sourceforge.net/p/ngspice/bugs/310/
h_vogt
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