Merge branch 'refs/heads/t/base64'

A couple of patches which move the base64 code to a separate file,
and improve on it. Was cooking for several months.

* refs/heads/t/base64:
  base64: Speed up decoder by using a table.
  base64: Use para_isspace() everywhere.
  base64: Trivial whitespace fixes.
  base64: Replace Pad64 variable by macro.
  base64: Remove unnecessary overflow checks.
  base64: Saner semantics for base64_decode() and uudecode().
  Move base64 implementation to own file.