Rework our index support.

* Add a new document-specific variable, HAS_INDEX, to specify if a
    given document is marked up with <indexterm> entries.

  * Rework the index support so that both HAS_INDEX and GEN_INDEX are
    checked before trying to generate an index for a document.

  * Only create index.sgml if both HAS_INDEX and GEN_INDEX are set.

This allows us to recursively build the documentation tree with
GEN_INDEX=1 and have it only try to create an index (very time
consuming) for the few documents that are ready for this.  Previously,
running "make GEN_INDEX=1" from the top of the doc tree would look for
index terms in every single document.

With this, I hope we can start building our docs with GEN_INDEX set on
freefall so that users browsing the HTML docs will get the benefit of
the index we've been hiding in CVS for 6 months.

en_US.ISO8859-1/books/arch-handbook/Makefile

@@ -10,11 +10,11 @@ DOC?= book
 
 FORMATS?= html-split
 
+HAS_INDEX= true
+
 INSTALL_COMPRESSED?= gz
 INSTALL_ONLY_COMPRESSED?=
 
-GEN_INDEX?= yes
-
 # Images
 IMAGES= sockets/layers.eps sockets/sain.eps sockets/sainfill.eps sockets/sainlsb.eps sockets/sainmsb.eps sockets/sainserv.eps sockets/serv.eps sockets/serv2.eps sockets/slayers.eps
 

en_US.ISO8859-1/books/developers-handbook/Makefile

@@ -10,11 +10,11 @@ DOC?= book
 
 FORMATS?= html-split
 
+HAS_INDEX= true
+
 INSTALL_COMPRESSED?= gz
 INSTALL_ONLY_COMPRESSED?=
 
-GEN_INDEX?= yes
-
 # Images
 IMAGES= sockets/layers.eps sockets/sain.eps sockets/sainfill.eps sockets/sainlsb.eps sockets/sainmsb.eps sockets/sainserv.eps sockets/serv.eps sockets/serv2.eps sockets/slayers.eps
 

en_US.ISO8859-1/books/handbook/Makefile

@@ -30,6 +30,8 @@ DOC?= book
 
 FORMATS?= html-split
 
+HAS_INDEX= true
+
 INSTALL_COMPRESSED?= gz
 INSTALL_ONLY_COMPRESSED?=
 

share/mk/doc.docbook.mk

@@ -25,6 +25,9 @@
 #			them need to be generated.  Changing any file in
 #			SRCS causes the documents to be rebuilt.
 #
+#       HAS_INDEX       This document has index terms and so an index
+#                       can be created if specified with GEN_INDEX.
+#
 
 # ------------------------------------------------------------------------
 #
@@ -47,9 +50,10 @@
 #
 #	NO_TIDY		If you do not want to use tidy, set this to "YES".
 #
-#       GEN_INDEX       If defined, index.sgml will be added to the list
+#       GEN_INDEX       If this document has an index (HAS_INDEX) and this
-#                       of dependencies for source files, and collateindex.pl
+#                       variable is defined, then index.sgml will be added 
-#                       will be run to generate index.sgml.
+#                       to the list of dependencies for source files, and 
+#                       collateindex.pl will be run to generate index.sgml.
 #
 #	CSS_SHEET	Full path to a CSS stylesheet suitable for DocBook.
 #			Default is ${DOC_PREFIX}/share/misc/docbook.css
@@ -323,14 +327,14 @@ CLEANFILES+= ${.CURDIR:T}.${_curformat}.${_curcomp}
 #
 # Index generation
 #
-INDEX_SGML?=		index.sgml
 CLEANFILES+= 		${INDEX_SGML}
 
-.if defined(GEN_INDEX)
+.if defined(GEN_INDEX) && defined(HAS_INDEX)
 JADEFLAGS+=		-i chap.index
 HTML_SPLIT_INDEX?=	html-split.index
 HTML_INDEX?=		html.index
 PRINT_INDEX?=		print.index
+INDEX_SGML?=		index.sgml
 
 CLEANFILES+= 		${HTML_SPLIT_INDEX} ${HTML_INDEX} ${PRINT_INDEX}
 .endif
@@ -471,13 +475,8 @@ lint validate:
 # an empty index.sgml file so that we can reference index.sgml in book.sgml
 #
 
-.if defined(GEN_INDEX)