"make mandocs" generate > 2000 files in Documentation/DocBook/man
and this caused kbuild to barf out during make mrproper like this:

make -f scripts/Makefile.clean obj=Documentation/DocBook
make -f scripts/Makefile.clean obj=Documentation/DocBook/man/
make[2]: execvp: /bin/sh: Argument list too long
make[2]: *** [__clean] Error 127
make[1]: *** [Documentation/DocBook/man/] Error 2
make: *** [_mrproper_Documentation/DocBook] Error 2

The man directory were solely used for output
so the fix is to remove it entirely during the
make mrproper process.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!