Add 6.3-RELEASE to the EoL table; it will be supported until the end of
January 2010.

Insert the same date as the estimated EoL for RELENG_6; if there turns
out to be a 6.4-RELEASE at some later date, the EoL for RELENG_6 will
be correspondingly extended, but unless/until the release engineering
team decides that 6.4-RELEASE will happen users should plan on moving
to RELENG_7 before the end of January 2010.