Accept import of abbreviations of gender

In 2.2.2, Import accepts only 'Male', 'Female' and 'Trangender' as gender values. This is limiting since it is commonplace to find eg. 'F' or 'f' as values for 'Female'. The attached patch causes import to accept any matching initial substring of the canonical gender value under case-insensitive comparison. Thus eg. 'f', 'female', 'F' are all accepted and converted to 'Female' during import.

For further study is i18n, to accept eg. 'varon' or 'mujer'.