Temp table does not support multi-language

[yuliarotenshtein]

The temp tables used by PL during fetch are created with the default charset and collation, therefore they do not support proper comparison of words in non-English languages .
This causes failures when trying to upsert a row keyed by a non-English string , when there us a similar English string already in the DB.

Please see test to reproduce this issue: https://github.com/kenshoo/kea/pull/158/