Made mask unsigned to avoid shifting into sign bit.

The last iteration of the loop execute 1<<63, which would push the
result into the signed bit of a signed 64 bit type, and this
move into currently undefined behaviour with C99.  Avoid the
issue by making the operation work on unsigned 64 bit type instead.

This require libogg version to 1.3.4, raise autotools dependency check
to look for this.

Partly solves github issue #18.