[STYLE] bfill and bzero vs memset

[Tor Didriksen]

Hi

I suggest we remove this recommendation from the style guide:

    For example, use |bfill()| and |bzero()| instead of |memset()|.

and that we use the standard memset() function.

reason: bzero has a number of problems
   - bzero does not seem to be well defined, I'm getting this during
     MySQL configure on Fedora release 12
     config.log:conftest.c:247: warning: conflicting types for built-in 
function 'bzero'
   - on some platforms it is not defined
   - on some platforms it is available, but in non-standard places
   - it was deprecated by posix 9 years ago
   - it is not part of the current posix standard
   - http://bugs.mysql.com/bug.php?id=55721
     where autoconf finds bzero() but the prototype is not visible when 
compiling, do the build fails

Implementation strategy: replace bfill() and bzero() with memset(),
merge changes into relevant trees.

-- didrik