bug fixed for gogs/gogs#3928 introduced by 64b3df6

resolved go-xorm#498

tag v0.5.6

small optimization

Merge pull request go-xorm#378 from gavv/master

Accumulate args when using Join() multiple times

join parameters support & many comments

resolved go-xorm#374

Merge pull request go-xorm#358 from denji/tokudb

Preventing the creation of duplicate index TokuDB

Merge branch 'master' of github.com:go-xorm/xorm

Merge pull request go-xorm#295 from aviau/patch-1

copyright: add owner