IMPALA-13: Use SSE string functions that take an explicit length

This patch modifies DelimitedTextParser and StringValue to work with
data containing null characters by using SSE instructions that take a
length, rather than expecting null-terminated strings. It also adds
some other minor changes to correctly handle data with nulls and to
faciliate testing. I checked the execution time of a count(*) and a
select(*) limit 1 query locally, and saw no difference for either text
or sequence files.

Change-Id: Ia920b35bea7048aa286f39ec83e313c2a39251d1
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2110
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: Skye Wanderman-Milne <skye@cloudera.com>