r17738: solving the seemingly trivial problem of timegm() being missing on

r17738: solving the seemingly trivial problem of timegm() being missing on
some systems requires quite a large change in ldb. The core problem is
that ldb doesn't have its own equivalent of lib/replace/, so we have
no sane place to put things like timegm.c

This patch moves part of lib/replace/ from Samba4 into ldb, and the
next patch will remove those parts from Samba4. We will probably need
to similarly move parts of lib/replace/ into lib/talloc/ and lib/tdb/,
so that at each level the libraries have replacements for the
functions they need, but higher level libraries don't need to
re-include replacements if a lower level library already replaces the
function
(This used to be commit c2f6c217fb4a5c84499246480f00df40b0711074)