plmkstrm: Creates a new stream and makes it the default

Creates a new stream and makes it the default. Differs from using plsstrm, in that a free stream number is found, and returned. Unfortunately, I have to start at stream 1 and work upward, since stream 0 is preallocated. One of the big flaws in the PLplot API is that no initial, library-opening call is required. So stream 0 must be preallocated, and there is no simple way of determining whether it is already in use or not.

p_strm (PLINT *, output) Pointer to stream number of the created stream.