Per Abdel's suggestion that we focus on bug-fixing at this point, this
will be the last patch in this series for a bit. But I wanted to get
this done before I forget what it is I was doing, so here it is.
The idea behind this patch is to make real key-value support for
InsetCommand parameter
It's now a pretty trivial matter to add proper keyval support, which
will make it possible to create a far better UI for e.g. the listings
parameters. Question: If a LaTeX command takes keyval-type arguments, is
it generally true that this will be true for only ONE of the arguments
