build: Fix AUTHORS generation

Using s/#authorslist#/$$out/ makes perl eat @domain part of all email
addresses from $out since it tries to interpret them as array variables.
I'm not sure if we can escape those in s/// but I know we can use print:

    s/#authorslist#// and print '$$out'

to tell perl not to even look inside $out.

This patch also fixes gen-AUTHORS so that it works in VPATH.

Makefile.am

@@ -95,9 +95,9 @@ gen-ChangeLog:
 
 .PHONY: gen-AUTHORS
 gen-AUTHORS:
-	$(AM_V_GEN)if test -d .git; then \
-	    out="`git log --pretty=format:'%aN <%aE>' | sort -u`" && \
-	    cat $(srcdir)/AUTHORS.in | perl -p -e "s/#authorslist#/$$out/" > \
-	      $(distdir)/AUTHORS-tmp && \
+	$(AM_V_GEN)if test -d $(srcdir)/.git; then \
+	    out="`cd $(srcdir) && git log --pretty=format:'%aN <%aE>' | sort -u`" && \
+	    perl -p -e "s/#authorslist#// and print '$$out'" \
+	      < $(srcdir)/AUTHORS.in > $(distdir)/AUTHORS-tmp && \
 	    mv -f $(distdir)/AUTHORS-tmp $(distdir)/AUTHORS ; \
 	fi