Fix undefined variable warning in md5.h

The attached patch fixes a -Wundef warning when compiling the current
svn version of libdvdread4 (as part of MPlayer) in the obvious way

Patch provided by Erik Auerswald <auerswal AT unix-ag DOT uni-kl DOT
de>. Thanks!
ignore generated files

Put a gitignore in that allows the user to not see the build generated
files when using git. Patch provided by Mike Frysinger. Thanks!
Remove the need for mkinstalldirs

Patch provided by KO Myung-Hun <komh78 AT gmail DOT com>. Thanks!