Mseedindex

- Increase maximum size of buffer allowed for the string representation
of the time spans (4 MiB to 8 MiB). Sufficient for 200,000+ spans.

- Increase maximum size of buffers allowed for the string representation
of the time index (1 KB to 4 KB) and time spans (1 MiB to 4 MiB).

- Separate file reading and database synchronization into different loops.
- Only connect to the database after all input files have been read.
This avoids holding a database connection open while data files are read
and reduces the connection time needed.

- Update libmseed to 2.15.
- Reset previous file position for each file.
- Track whether records in a data section are in time order and set
a 'latest' flag in the time index based on ordering. If the records
are in time order then the index also indicates the byte offest of the
latest timed data.

- Update libmseed to 2.14.
- Read leap second list file from /opt/dmc/share/leap-seconds.list

- Set data section update time to file modification time instead of
the scan time when not retaining an existing entry.