Change the way the value of DESTDIR is determined for the release

notes build. Instead of having doc.relnotes.mk make a guess, hardcode
quite a bit (but as little as possible) in Makefile.inc's sprinkled
strategicly throughout the tree.  This has the advantage of actually
working properly (which is a Good Thing(tm)), and the disadvantages of
more files in the repository and more hardcoded paths (which are both
Bad Things(tm)).

release/doc/en_US.ISO8859-1/errata/Makefile

@@ -1,6 +1,7 @@
 # $FreeBSD$
 
 RELN_ROOT?= ${.CURDIR}/../..
+DESTDIR?= ${DOCDIR}/en_US.ISO8859-1/errata
 
 DOC?= article
 FORMATS?= html

release/doc/en_US.ISO8859-1/hardware/Makefile.inc

@@ -0,0 +1,3 @@
+# $FreeBSD$
+
+DESTDIR?=	${DOCDIR}/en_US.ISO8859-1/hardware/${.CURDIR:T}

release/doc/en_US.ISO8859-1/installation/Makefile.inc

@@ -0,0 +1,3 @@
+# $FreeBSD$
+
+DESTDIR?=	${DOCDIR}/en_US.ISO8859-1/installation/${.CURDIR:T}

release/doc/en_US.ISO8859-1/readme/Makefile

@@ -1,6 +1,7 @@
 # $FreeBSD$
 
 RELN_ROOT?= ${.CURDIR}/../..
+DESTDIR?= ${DOCDIR}/en_US.ISO8859-1/readme
 
 DOC?= article
 FORMATS?= html

release/doc/en_US.ISO8859-1/relnotes/Makefile.inc

@@ -0,0 +1,3 @@
+# $FreeBSD$
+
+DESTDIR?=	${DOCDIR}/en_US.ISO8859-1/relnotes/${.CURDIR:T}

release/doc/share/mk/doc.relnotes.mk

@@ -8,9 +8,3 @@ EXTRA_CATALOGS+= ${RELN_ROOT}/share/sgml/catalog
 # Use the appropriate architecture-dependent RELNOTESng stylesheet
 DSLHTML?=	${RELN_ROOT}/en_US.ISO8859-1/share/sgml/release.dsl
 DSLPRINT?=	${RELN_ROOT}/en_US.ISO8859-1/share/sgml/release.dsl
-
-# XXX It may be possible to get this right just about all of the time
-# using ${RELN_ROOT}; "/release/doc" is just something that (I think)
-# covers the majority of the cases.
-RELN_ANCHOR?=	/release/doc/
-DESTDIR?= ${DOCDIR}/${.CURDIR:C/^.*${RELN_ANCHOR}/}