mkfifo/fopen/fread/fwrite kind of worked with glibc 2.26 and gcc 7.2.0.
  With 2.28 named-pipe reading with fread would read the pipe only once for
  some reason - probably because it stopped being a 'blocking' call
  To fix - switched to open/read/poll combination - so none of glibc functions
  is used.

2. camogm_fifo_reader - test program - use with *_writer or just 'echo'
3. camogm_fifo_writer - test program

 Conflicts:
	src/camogm.c
	src/camogm.h

This commit also adds sensor port number to last_error_code returned in
xml status report.