Allow identical lines in import

[jzohrab]

Currently the term import fails if the same term is listed twice, e.g. in tests/features/term_import:

    Scenario: Duplicate term throws
        Given import file:
            language,term
            Spanish,gato
            Spanish,gato
        Then import should fail with message:
            Duplicate terms in import: Spanish: gato

Really, this should only be a problem if there is inconsistent data. e.g, this is bad:

    Scenario: Duplicate term throws
        Given import file:
            language,term,translation
            Spanish,gato,cat
            Spanish,gato,kitty
        Then import should fail with message:
            Duplicate terms in import: Spanish: gato

but this should work:

    Scenario: identical lines ok
        Given import file:
            language,term
            Spanish,gato,cat
            Spanish,gato,cat
        Then import should succeed with 1 term imported

[jzohrab]

fixed in develop with test case.

[jzohrab]

Released in 3.6.1.