FreeBSD/src 13ff4eb (r350204)share/man/man9 refcount.9, sys/sys refcount.h

Switch the rest of the refcount(9) functions to bool return type.

There are some explicit comparisions of refcount_release(9) result
with 0/1, which are fine.

Reviewed by:    markj, mjg
Sponsored by:   The FreeBSD Foundation
MFC after:      1 week
Differential revision:  https://reviews.freebsd.org/D21014
DeltaFile
+9-9sys/sys/refcount.h
+5-5share/man/man9/refcount.9
+14-142 files

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