Parse regions without begin/end as 1..MAX_INT rather than 1..2^29

Indexing now works with large chromosomes (longer than 2^29) both when
coordinates are specified ("foo:1000-600,000,000") and when they are
defaulted to the whole chromosome ("foo").

For hts_itr_querys("."), HTS_IDX_START ignores begin/end, so pass these
as 0,0 rather than a misleading 1<<29.

/<< *29/ no longer appears in the htslib source code.

Fixes part 2 of samtools/samtools#241.