[Libguestfs] [PATCH] v2v: Make the interface between cmdline.ml and v2v.ml

I'm interested to hear opinions on whether this makes the code clearer, or not. This is virt-v2v, but many other virt-* tools work the same way, and analogous changes could be made. Currently when command line argument parsing is done in 'cmdline.ml' the list of parsed parameters is passed to the main program in a very long tuple. Each parameter is strongly typed, but not named (so for example two 'bool' flags on the command line might be swapped accidentally). This patch uses a struct to pass the parameters instead, so they are both strongly typed *and* named - two parameters with the same type could not be swapped by accident. Also the type of each parameter is now defined in the struct 'type' definition, which also appears in a 'cmdline.mli' file. In addition, in the main program it should be clearer where a particular variable comes from, ie. you have to write 'cmdline.output_alloc' instead of 'output_alloc', which may make it clearer that it comes from the command line '-oa' parameter, thus making the code easier to understand. Rich.