This was an early way of resolving tag values that is now obsolete.
`ValueContext` structs should be used, and these, in many cases, should
be able to be constructed from the current context without passing
additional arguments.
- ifd_builder_test.go: Refactors to several tests due to loss of ITEVR support.
- ifd_builder_encode_test.go: Moved test-IB populate to testing_common.go .
- ifd_builder.go: Fixed test naming (in most cases, omitted type name).
Dustin Oprea