Documenting opt.Options.Comparer
Documenting opt.Options.Comparer

Since I just added documentation for changing filter, I also thought
about commenting on the fact that Comparer must not be changed after
creation of a database.

conseweb/goleveldb,ngaut/goleveldb,hustbill/goleveldb,syndtr/goleveldb,no2key/goleveldb,btcsuite/goleveldb,zzl0/goleveldb,chai2010/goleveldb,trigrass2/goleveldb,FactomProject/goleveldb,rentongzhang/goleveldb