build: Allow OCaml programs using libguestfs to be compiled against build dir.

You have to use:
  ../libguestfs/run ./configure
  ../libguestfs/run make

Use of the second ../libguestfs/run against make is unfortunate but I
believe it's unavoidable due to the way that ocamlfind works.

.gitignore

@@ -379,6 +379,7 @@ Makefile.in
 /ocaml/examples/guestfs-ocaml.3
 /ocaml/examples/inspect_vm
 /ocaml/examples/stamp-guestfs-ocaml.pod
+/ocaml/guestfs
 /ocaml/guestfs-c-actions.c
 /ocaml/guestfs-c-errnos.c
 /ocaml/guestfs.ml

ocaml/Makefile.am

@@ -197,4 +197,21 @@ install-data-hook:
 
 CLEANFILES += $(noinst_DATA) $(check_DATA)
 
-endif
+# This "tricks" ocamlfind into allowing us to compile other OCaml
+# programs against a locally compiled copy of the libguestfs sources.
+# ocamlfind needs to see a directory called ‘guestfs’ which contains
+# ‘META’.  The current directory is called ‘ocaml’, but if we make
+# this symlink then we can create the required directory structure.
+#
+# Note if you just want to use this, make sure you use
+# ‘../libguestfs/run make’ in your other program and everything should
+# just work.
+CLEANFILES += guestfs
+
+all-local: guestfs
+
+guestfs:
+	rm -f $@
+	$(LN_S) . $@
+
+endif HAVE_OCAML

run.in

@@ -227,6 +227,8 @@ export MALLOC_PERTURB_=$random_val
 # local libguestfs.
 prepend PKG_CONFIG_PATH "$b/lib/local"
 export PKG_CONFIG_PATH
+prepend OCAMLPATH "$b/ocaml"
+export OCAMLPATH
 
 # Do we have libtool?  If we have it then we can use it to make
 # running valgrind simpler.  However don't depend on it.