Add a compiler flag to disable string pooling

[MarkPflug]

This PR adds a global compiler flag to easily toggle "string pooling" on and off for the small number of libraries that support it. For "realistic" data sets string pooling would most likely slow things down. It is only beneficial here because of how the data set is created by repeating a relatively small number of rows. This leaves pooling enabled, so future runs will be consistent with past results.

[leandromoh]

@MarkPflug , dont forget RecordParser. You can find by searching "var cache = new InternPool();"

[joelverhagen]

Looks great, thanks Mark! And @leandromoh, I'll do a pass over all tests to double check this applies to RecordParser and other libraries properly.