Import openat, fdopendir and fstatat implementations into compat.c
Replace open with openat
Replace lstat with fstatat
Replace opendir with fdopendir
Garbage collect old open/readdir/stat code
Do not store path to watched file anymore
Move inode number from dep-list to i_watch and define dep-list only for
directories
Improve directory reopening code path
Block SIGPIPE for worker thread
Refactor creation of communication pipe