Fix mis-matched types for serialno's.

The use of long caused some functions which now use libogg's
 ogg_page_serialno() (which returns an int) to sign-extend the
 serialno, while the actual list was stored as ogg_uint32_t's.
This would cause subsequent lookups to fail on platforms with a
 64-bit long.
Introduced in r17375 and r16259, but only partially corrected in
 r17536.
Fixes #1838.
Thanks to achurch for the report.


git-svn-id: https://svn.xiph.org/trunk/Tremor@18116 0101bb08-14d6-0310-b084-bc0e0c8e3800