Use the USERS/GROUPS mechanism for the boinc-client port instead of
manually creating them.
It is still possible to overrride the defaults by setting
BOINC_CLIENT_USER , BOINC_CLIENT_GROUP , and BOINC_CLIENT_HOME but that
means the entries in UIDs and GIDs have to be changed too.
PR: ports/176274 (part, based on)
Submitted by: Andrey Simonenko <email@example.com>
Reviewed by: crees (slightly)