1. Call the internal variable portname (like pidname) everywhere.
2. Have a variable wroteportfile (like wrotepidfile) everywhere.
3. Make sure the file is cleaned up on exit (like pidfile).
4. Add parameter --portfile to usage outputs everywhere.
Reviewed-by: Daniel Stenberg
Replaces #7523Closes#7574
Mark global variables static to avoid compiler warning in Clang when
using -Wmissing-variable-declarations.
Closes#3778
Reviewed-by: Daniel Stenberg <daniel@haxx.se>
