Prefer SRCTOP over CURDIR/../../contrib, etc. However, retain the "up
one level" instances of ../ because they are really relative to this
part of the tree and not a means to find the root of the tree. As
such, it's better to leave them since that further the goal of being
able to move directories if watned to in the future.
Differential Revision: https://reviews.freebsd.org/D9932
Sponsored by: Netflix
Silence On: arch@ (twice)
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