fetchmail: fixup md5 transition

fetchmail: fixup md5 transition

this patch is cherry-pick from upstream:
  http://gitorious.org/fetchmail/fetchmail/commit/738dcc102db67a741893e2979c034df9904e2925

this patch fixed this error:
  http://tksite.gotdns.org:8010/broken_packages/xburst/fetchmail/compile.txt
~~~
mipsel-openwrt-linux-uclibc-gcc -DHAVE_CONFIG_H -DLOCALEDIR=\"/usr/share/locale\" -I.  -I./libesmtp -I/home/buildslave/openwrt1/xburst/build/staging_dir/target-mipsel_uClibc-0.9.31/usr/include -I/home/buildslave/openwrt1/xburst/build/staging_dir/target-mipsel_uClibc-0.9.31/include -I/home/buildslave/openwrt1/xburst/build/staging_dir/toolchain-mipsel_gcc-4.3.3+cs_uClibc-0.9.31/usr/include -I/home/buildslave/openwrt1/xburst/build/staging_dir/toolchain-mipsel_gcc-4.3.3+cs_uClibc-0.9.31/include   -Os -pipe -mips32 -mtune=mips32 -funit-at-a-time -fhonour-copts -msoft-float  -MT md5c.o -MD -MP -MF .deps/md5c.Tpo -c -o md5c.o md5c.c
md5c.c:44: warning: 'struct MD5Context' declared inside parameter list
md5c.c:44: warning: its scope is only this definition or declaration, which is probably not what you want
md5c.c: In function 'MD5Init':
md5c.c:46: error: dereferencing pointer to incomplete type
md5c.c:47: error: dereferencing pointer to incomplete type
~~~

SVN-Revision: 25228