Add autofiles.zip make target

This target creates autofiles.zip from a source distribution or fresh
checkout after autogen.sh has been run.  The resulting zip can be
unzipped over a fresh checkout to support easier building on Windows
from a clean checkout.

.gitignore

@@ -1,5 +1,6 @@
 aclocal.m4
 autoconf.mk
+autofiles.zip
 autom4te.cache/
 config.log
 config.status

Makefile

@@ -91,6 +91,11 @@ $(foreach B,$(BUILD_ITEMS),$(eval \
   clean_$(B): ; \
 	$(RM) -r $(B)/$(OUTPUT_DIR)))
 
+AUTOFILES = configure aclocal.m4 libqpdf/qpdf/qpdf-config.h.in
+autofiles.zip: $(AUTOFILES)
+	$(RM) autofiles.zip
+	zip autofiles.zip $(AUTOFILES)
+
 distclean: clean
 	$(RM) -r autoconf.mk autom4te.cache config.log config.status libtool
 	$(RM) libqpdf/qpdf/qpdf-config.h
@@ -103,6 +108,7 @@ maintainer-clean: distclean
 	$(RM) configure doc/qpdf-manual.* libqpdf/qpdf/qpdf-config.h.in
 	$(RM) aclocal.m4
 	$(RM) -r install-mingw install-msvc external-libs
+	$(RM) autofiles.zip
 
 .PHONY: $(TEST_TARGETS)
 $(foreach B,$(TEST_ITEMS),$(eval \

README-windows.txt

@@ -77,6 +77,18 @@ You can also download qpdf-external-libs-src.zip and follow the
 instructions in the README.txt there for how to build external libs.
 
 
+Building from version control
+=============================
+
+If you check out qpdf from version control, you will not have the
+files that are generated by autoconf.  If you are not changing these
+files, you can grab them from a source distribution or create them
+from a system that has autoconf.  To create them from scratch, run
+./autogen.sh on a system that has autoconf installed.  Once you have
+them, you can run make CLEAN=1 autofiles.zip.  This will create an
+autofiles.zip that you can extract on top of a fresh checkout.
+
+
 Building with MinGW
 ===================