TST: fix test_decimal_builtins_2 for py26 (again)
TST: fix test_decimal_builtins_2 for py26 (again)

Some of the expressions return Decimal values while some return floats, which need to be handled separately.

mariusvniekerk/ibis,Supermem/ibis,laserson/ibis,wesm/ibis,ashhher3/ibis,deepfield/ibis,wesm/ibis,laserson/ibis,fivejjs/ibis,koverholt/ibis,glenioborges/ibis,dalejung/ibis,dalejung/ibis,korotkyn/ibis,laserson/ibis,fivejjs/ibis,cpcloud/ibis,ashhher3/ibis,ibis-project/ibis,mahantheshhv/ibis,glenioborges/ibis,cpcloud/ibis,korotkyn/ibis,Supermem/ibis,fivejjs/ibis,dalejung/ibis,dboyliao/ibis,cloudera/ibis,aslihandincer/ibis,korotkyn/ibis,mariusvniekerk/ibis,ashhher3/ibis,adamobeng/ibis,deepfield/ibis,mariusvniekerk/ibis,shaunstanislaus/ibis,glenioborges/ibis,ibis-project/ibis,Winterflower/ibis,dboyliao/ibis,glenioborges/ibis,Winterflower/ibis,adamobeng/ibis,shaunstanislaus/ibis,aslihandincer/ibis,deepfield/ibis,deepfield/ibis,shaunstanislaus/ibis,ibis-project/ibis,laserson/ibis,cpcloud/ibis,mahantheshhv/ibis,cloudera/ibis,adamobeng/ibis,Supermem/ibis,o0neup/ibis,aslihandincer/ibis,ashhher3/ibis,adamobeng/ibis,aslihandincer/ibis,ibis-project/ibis,mahantheshhv/ibis,mariusvniekerk/ibis,cloudera/ibis,cpcloud/ibis,wesm/ibis,Supermem/ibis,koverholt/ibis,o0neup/ibis,Winterflower/ibis,korotkyn/ibis,dboyliao/ibis,mahantheshhv/ibis,koverholt/ibis,koverholt/ibis,dboyliao/ibis,o0neup/ibis