Avoid hard-coded "%ld" format strings in mod_deflate's logging statements.

On some platforms (e.g. OpenBSD) zlib's input/output counters are off_t
instead of ulong, which resuls in format-string warnings from some
compilers (e.g. clang). Work around this by upcasting to uint64_t.
Discussed on dev@ with ylavic and wrowe


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1849590 13f79535-47bb-0310-9956-ffa450edef68