Function `dayno` shares name with many variables

[aburrell]

Line 308 in codebase/general/src.lib/time.1.7/src/time.c has a function named dayno. This name is also frequently used as a variable and a structure element name. Apart from the code confusion, this hinders compliation in some scenarions. I'd recommend renaming this function to something like calc_dayno.

Originally posted by @aburrell in #630 (comment)