Thr first bunch of changes replaces install-data-local with
install-data-hooks. I, Martin von Gagern, at the time I'm writing this
header, don't fully comprehend the reason behind this.  The original patch
by Gilles Dartiguelongue contained no header at all. See the references
below for updates on this.

The second issue seems to be caused by the following scenario:
 * install-data-local (now install-data-hooks) depends on both
   install-doc-docs and install-doc-pdf.
 * both these targets create their output subdirectories using mkinstalldirs.
 * install-sh seems to have provisions for concurrent execution, but only
   when installing files, not when invoked to create directories.

The patch addresses the issue by having install-doc-pdf not create any
directories itself, but depend on install-doc-docs to do that.

As an alternative, it might be possible to drop the explicit directory
creation altogether, and rely on the implicit and concurrency-aware
directory creation of install-sh. The patch below is closer to original
behaviour, and thus may be more portable, even in cases where install-sh
would not be concurrency-aware.

2009-01-11 Gilles Dartiguelongue
2009-03-06 Martin von Gagern

References:
https://bugs.gentoo.org/252163
https://bugs.gentoo.org/260827

Index: gnome-user-docs-2.24.2/gnome2-accessibility-guide/Makefile.am
===================================================================
--- gnome-user-docs-2.24.2.orig/gnome2-accessibility-guide/Makefile.am
+++ gnome-user-docs-2.24.2/gnome2-accessibility-guide/Makefile.am
@@ -14,13 +14,12 @@ DOC_ENTITIES =			\
 
 DOC_LINGUAS = de el en_GB es fi fr hu it oc pt sv
 
-install-data-local: install-doc-pdf
-install-doc-pdf:
+install-data-hook: install-doc-pdf
+install-doc-pdf: install-doc-docs
 	for lc in C $(DOC_LINGUAS); do \
 	  pdf="$$lc/$(DOC_MODULE).pdf"; \
 	  if [ -f "$$pdf" ]; then spdf="$$pdf"; else spdf="$(srcdir)/$$pdf"; fi; \
 	  if [ -f "$$spdf" ]; then \
-	    $(mkinstalldirs) "$(DESTDIR)$(HELP_DIR)/$(DOC_MODULE)/$$lc"; \
 	    $(INSTALL_DATA) "$$spdf" "$(DESTDIR)$(HELP_DIR)/$(DOC_MODULE)/$$pdf"; \
 	  fi; \
 	done
Index: gnome-user-docs-2.24.2/gnome2-user-guide/Makefile.am
===================================================================
--- gnome-user-docs-2.24.2.orig/gnome2-user-guide/Makefile.am
+++ gnome-user-docs-2.24.2/gnome2-user-guide/Makefile.am
@@ -17,13 +17,12 @@ DOC_INCLUDES =			\
 
 DOC_LINGUAS = ar bg de el es fi fr hu it ja ko oc pa pt pt_BR ru sv th zh_CN
 
-install-data-local: install-doc-pdf
-install-doc-pdf:
+install-data-hook: install-doc-pdf
+install-doc-pdf: install-doc-docs
 	for lc in C $(DOC_LINGUAS); do \
 	  pdf="$$lc/$(DOC_MODULE).pdf"; \
 	  if [ -f "$$pdf" ]; then spdf="$$pdf"; else spdf="$(srcdir)/$$pdf"; fi; \
 	  if [ -f "$$spdf" ]; then \
-	    $(mkinstalldirs) "$(DESTDIR)$(HELP_DIR)/$(DOC_MODULE)/$$lc"; \
 	    $(INSTALL_DATA) "$$spdf" "$(DESTDIR)$(HELP_DIR)/$(DOC_MODULE)/$$pdf"; \
 	  fi; \
 	done
Index: gnome-user-docs-2.24.2/gnome2-system-admin-guide/Makefile.am
===================================================================
--- gnome-user-docs-2.24.2.orig/gnome2-system-admin-guide/Makefile.am
+++ gnome-user-docs-2.24.2/gnome2-system-admin-guide/Makefile.am
@@ -20,13 +20,12 @@ DOC_ENTITIES =			\
 
 DOC_LINGUAS = ca de el es fi fr it ja ko oc pa pt sv zh_CN
 
-install-data-local: install-doc-pdf
-install-doc-pdf:
+install-data-hook: install-doc-pdf
+install-doc-pdf: install-doc-docs
 	for lc in C $(DOC_LINGUAS); do \
 	  pdf="$$lc/$(DOC_MODULE).pdf"; \
 	  if [ -f "$$pdf" ]; then spdf="$$pdf"; else spdf="$(srcdir)/$$pdf"; fi; \
 	  if [ -f "$$spdf" ]; then \
-	    $(mkinstalldirs) "$(DESTDIR)$(HELP_DIR)/$(DOC_MODULE)/$$lc"; \
 	    $(INSTALL_DATA) "$$spdf" "$(DESTDIR)$(HELP_DIR)/$(DOC_MODULE)/$$pdf"; \
 	  fi; \
 	done