And the final bit of VUFIND-1004.
Added more x51 subfields to index mappings.
Merge branch 'release-2.3'
Revert "And the final bit of VUFIND-1004." (not meant for 2.3)

This reverts commit 4044ed4bd16efff5dacd506f4bd2302f916ffca3.
Merge branch 'release-2.3'
Putting reverted changes from 2.3 branch back into master. Ah, the confusion!

Revert "Revert "And the final bit of VUFIND-1004." (not meant for 2.3)"

This reverts commit e6b24af97fae62b15c1a6f8e8cefb58ff82fe982.