Add a --disable-man configure option

OSTree doesn't have DocBook stylesheets, so generating
man pages from xml causes build failures there.

Makefile.am

@@ -1,7 +1,11 @@
 # Point to our macro directory and pick up user flags from the environment
 ACLOCAL_AMFLAGS  = -I m4 ${ACLOCAL_FLAGS}
 
-SUBDIRS = data js src browser-plugin tests po man docs
+SUBDIRS = data js src browser-plugin tests po docs
+
+if ENABLE_MAN
+SUBDIRS += man
+endif
 
 EXTRA_DIST =		\
 	.project	\
@@ -21,4 +25,4 @@ distcheck-hook:
 	@echo "Checking disted files against files in git"
 	@$(srcdir)/tools/check-for-missing.py $(srcdir) $(distdir) $(DIST_EXCLUDE)
 
-DISTCHECK_CONFIGURE_FLAGS = --enable-gtk-doc
+DISTCHECK_CONFIGURE_FLAGS = --enable-gtk-doc --enable-man

configure.ac

@@ -209,6 +209,18 @@ AC_SUBST(TYPELIBDIR)
 
 GTK_DOC_CHECK([1.15], [--flavour no-tmpl])
 
+AC_ARG_ENABLE(man,
+              [AS_HELP_STRING([--enable-man],
+                              [generate man pages [default=yes]])],,
+              enable_man=yes)
+if test "$enable_man" != no; then
+  AC_PATH_PROG([XSLTPROC], [xsltproc])
+  if test -z "$XSLTPROC"; then
+    AC_MSG_ERROR([xsltproc is required for --enable-man])
+  fi
+fi
+AM_CONDITIONAL(ENABLE_MAN, test "$enable_man" != no)
+
 # Stay command-line compatible with the gnome-common configure option. Here
 # minimum/yes/maximum are the same, however.
 AC_ARG_ENABLE(compile_warnings,