Fix building manpages in parallel build dirs

Commit 2ebb3cf introduced an issue
when building manpages in parallel build dirs. It unnecessarily
modified the XML_DOC definition to restrict it to basing its
contents on the man_MANS variable. Unfortunately, this means that
when we entered the recursion in all-local we would be effectively
turning XML_DOC into $(srcdir)/$(lang)/manpage.N.xml when we really
only care that the source language XML document exists.

This patch reverts that portion of the change.

https://fedorahosted.org/sssd/ticket/1293

src/man/Makefile.am

@@ -93,7 +93,7 @@ EXTRA_DIST += \
 	$(POTFILE)\
 	$(PO4A_CONFIG)
 
-XML_DOC = $(man_MANS:%=$(srcdir)/%.xml) $(wildcard $(srcdir)/include/*.xml)
+XML_DOC = $(wildcard $(srcdir)/*.xml) $(wildcard $(srcdir)/include/*.xml)
 
 if HAVE_PO4A