src/fieldsplit: perf enhancements.
src/fieldsplit: perf enhancements.

- cache the output filehandles if they are likely to be written
  to. This is captured during the writes, 10% of files that get a high
  degree of writes are left open.

- compile the xform regexs.

- use the get_line_field perf tuned function for getting line values.

google/crush-tools,lexsf/crush-tools,lexsf/crush-tools,google/crush-tools,lexsf/crush-tools,google/crush-tools,google/crush-tools,google/crush-tools,google/crush-tools,lexsf/crush-tools,google/crush-tools,lexsf/crush-tools,lexsf/crush-tools,lexsf/crush-tools