change echo to printf and for sfeed_opml_export use a control-character separator

echo is unportable in this way and names containing characters like an option
(-n) or backslash or escape codes (\e, \n, etc) could be messy.

For awk set LC_ALL=C for simple collation.

This makes sfeed_opml_export slower in some shells that don't have printf
builtin though. For example with about 150 feeds in a config file it is a bit
slower on OpenBSD ksh.

time ./sfeed_opml_export | wc -l
     152

    0m00.29s real     0m00.05s user     0m00.20s system

time sfeed_opml_export | wc -l
     152
    0m00.02s real     0m00.00s user     0m00.03s system

0 files changed, 0 insertions, 0 deletions