This file is a bit of a grab-bag of dict-wide API functions like
ctf_set_open_errno or ctf_errwarning_next and portabilty functions and
wrappers like ctf_mmap or ctf_pread.
Split the latter out, and move other dict-wide functions that got
stuck in ctf-util.c (because it was so hard to tell the two files
apart) into ctf-api.c where they belong.
