icepack_therm_vertical: add new local variables `delt`, `deltq` instead of using `worka`, `workb` about icepack HOT 1 OPEN

Changing the names of local variables is fine with me, if it makes the code easier to follow. Reusing work arrays was originally to minimize memory use but we can hardly claim to be efficient with that anymore.

intent(inout) was used to prevent an extra copy when passing arguments in and out of subroutines, and so was used throughout the code for this small bit of computational efficiency gain. For some reason, intent(out) did an extra copy that (inout) didn't have to do. I'm not sure whether this is still an issue with newer compilers. The tradeoff, of course, is some confusion about whether the variable actually needs to be passed in. I used it as a convenient excuse for gathering initializations into one code block in a higher routine.

from icepack.