Add hint to response behaviour when some user data is invalid.
Add hint to response behaviour when some user data is invalid.

willmclaren/ensembl-rest,ens-lgil/ensembl-rest,helensch/ensembl-rest,ens-lgil/ensembl-rest,willmclaren/ensembl-rest,willmclaren/ensembl-rest,helensch/ensembl-rest,willmclaren/ensembl-rest,ens-lgil/ensembl-rest,helensch/ensembl-rest,helensch/ensembl-rest,willmclaren/ensembl-rest,ens-lgil/ensembl-rest,helensch/ensembl-rest,ens-lgil/ensembl-rest