add --daemon option to serve command. for issue 45. code looks odd because it is portable to windows. windows does not have os.fork, so have to spawn and use pipe to tell parent ready instead.

adding foo
adding bomb
adding a.c
adding dir/a.o
adding dir/b.o
! a.c
! dir/a.o
! dir/b.o
? .hgignore
a.c: unsupported file type (type is fifo)
! a.c