Allow use alternative to default system SED program - SED4OMK.

Allow use alternative to default system SED program - SED4OMK.

This is required on BSD system derivatives (i.e. Apple MAC OS X)
where default sed program or its default mode does not interpret
vertical bar/pipe as text alternatives separator.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>