Commit Briefs
lib9: move seek into open.c
More preparation for opendir.
lib9: merge create, open, dirread into open.c
Preparation for using opendir.
lib9: make a p9frexp function wrapping system frexp
Under certain conditions it looks like frexp gets #defined to something else on macOS during system headers, which then breaks the declaration in libc.h.
lib9: remove getcallerpc implementations
These make no sense and are not really needed at all. Add a best-effort attempt to get at the gcc/clang macro in lib9.h, but if it fails, no big deal. Fixes #324.
lib9: import frand function from Plan 9
Fixes #15.