Here's a patch to import the md5 module from gnulib into Emacs.
I haven't committed this yet, as I would like to test it more,
but thought I'd give a heads-up.

For Windows, I expect the hand-generated makefiles will need to be
changed to compile lib/md5.c instead of src/md5.c, since the file was
moved.

The patch that I wrote is below.  I'm attaching the full patch
(including automatically generated changes), as a compressed file.

Import crypto/md5 module from gnulib.
* Makefile.in (MAKEFILE_MODULES): Add crypto/md5.
* admin/notes/copyright: Remove src/md5.c and src/md5.h as
special cases.
* src/Makefile.in (base_obj): Remove md5.o, since this file
is in lib now.
* src/deps.mk (md5.o): Remove.
* aclocal.m4, configure, lib/Makefile.in, lib/gnulib.mk, m4/gl-comp.m4:
Regenerate.
* lib/md5.c: Regenerate.  This renames the file from src/md5.c,
and adds some porting improvements from gnulib.
* lib/md5.h: Regenerate, likwise; rename from src/md5.h.
* m4/md5.m4: New file, from gnulib.

=== modified file 'Makefile.in'
--- Makefile.in	2011-02-16 01:35:20 +0000
+++ Makefile.in	2011-02-18 07:45:14 +0000
@@ -330,7 +330,8 @@
 # Update modules from gnulib, for maintainers, who should have it in
 # $(gnulib_srcdir) (relative to $(srcdir) and should have build tools
 # as per $(gnulib_srcdir)/DEPENDENCIES.
-GNULIB_MODULES = dtoastr getloadavg getopt-gnu ignore-value mktime strftime
+GNULIB_MODULES = \
+  crypto/md5 dtoastr getloadavg getopt-gnu ignore-value mktime strftime
 GNULIB_TOOL_FLAGS = \
  --import --no-changelog --no-vc-files --makefile-name=gnulib.mk
 sync-from-gnulib: $(gnulib_srcdir)

=== modified file 'admin/notes/copyright'
--- admin/notes/copyright	2011-02-16 01:35:20 +0000
+++ admin/notes/copyright	2011-02-18 07:45:14 +0000
@@ -632,8 +632,6 @@
     lib/*.[ch]
     lib/gnulib.mk
     src/gmalloc.c
-    src/md5.c
-    src/md5.h
     src/termcap.c
     src/tparam.c


=== modified file 'src/Makefile.in'
--- src/Makefile.in	2011-02-10 03:20:52 +0000
+++ src/Makefile.in	2011-02-18 07:45:14 +0000
@@ -354,7 +354,7 @@
 	syntax.o $(UNEXEC_OBJ) bytecode.o \
 	process.o gnutls.o callproc.o \
 	region-cache.o sound.o atimer.o \
-	doprnt.o intervals.o textprop.o composite.o md5.o xml.o \
+	doprnt.o intervals.o textprop.o composite.o xml.o \
 	$(MSDOS_OBJ) $(MSDOS_X_OBJ) $(NS_OBJ) $(CYGWIN_OBJ) $(FONT_OBJ)
 obj = $(base_obj) $(NS_OBJC_OBJ)


=== modified file 'src/deps.mk'
--- src/deps.mk	2011-02-16 01:35:20 +0000
+++ src/deps.mk	2011-02-18 07:45:14 +0000
@@ -144,7 +144,6 @@
 ralloc.o: ralloc.c lisp.h $(config_h)
 vm-limit.o: vm-limit.c mem-limits.h lisp.h globals.h $(config_h)
 marker.o: marker.c buffer.h character.h lisp.h globals.h $(config_h)
-md5.o: md5.c md5.h $(config_h)
 minibuf.o: minibuf.c syntax.h frame.h window.h keyboard.h systime.h \
    buffer.h commands.h character.h msdos.h $(INTERVALS_H) keymap.h \
    termhooks.h lisp.h globals.h $(config_h) coding.h