clean up docs build a little; have docdir be an overridable install location; separate gtk-doc and docbook bits

Original commit message from CVS:
clean up docs build a little; have docdir be an overridable install location; separate gtk-doc and docbook bits
diff --git a/Makefile.am b/Makefile.am
index 2e2adbe..94353a3 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,12 +1,6 @@
 PACKAGE = @PACKAGE@
 VERSION = @VERSION@
 
-if BUILD_DOCS
-SUBDIRS_DOCS = docs
-else
-SUBDIRS_DOCS =
-endif
-
 if BUILD_TESTS
 ## SUBDIRS_TESTS = tests testsuite
 ## FIXME: write tests from scratch
@@ -44,9 +38,9 @@
 	$(SUBDIRS_CHECK) \
 	$(SUBDIRS_TESTS) \
 	$(SUBDIRS_EXAMPLES) \
+	docs \
 	pkgconfig po \
-	common \
-	$(SUBDIRS_DOCS)
+	common
 
 # These are all the possible subdirs
 DIST_SUBDIRS = \
@@ -55,10 +49,10 @@
 	check \
 	tests testsuite \
 	examples \
+	docs \
 	pkgconfig \
 	po \
-	common \
-	docs
+	common
 
 win32 = $(shell cat $(top_srcdir)/win32/MANIFEST)