Support for PostgreSQL 9.3.
Rename of quantile-1.1.sql to quantile-1.1.1.sql (without this,
commit bfddd1f5 actually doesn't work).
Significant decrease of SLICE_SIZE (from 1024 to 5).

The original value often caused OOM even with rather small number
of groups (as it always allocated ~4kB of memory for each group,
even if there was a single item in each group). The new value is
much more conservative and it's actually faster in most tests.