Convert to unicode the string of predefined search field

DomainParser expect to work with unicode and gettext return string encoded in
utf-8 (coding of the po file)

issue3440
review1301002
(transplanted from 2bbb22151fc09ecbc9da17302def0fa111eb620f)

--HG--
extra : transplant_source : %2B%BB%22%15%1F%C0%9E%CB%C9%DA%170-%EF%0F%A1%11%EBb%0F
Dict widget must use rec_name to search key

review1401002
(transplanted from c909bd88517dc3752017b700901fe3d4a2ff2674)

--HG--
extra : transplant_source : %C9%09%BD%88Q%7D%C3u%20%17%B7%00%90%1F%E3%D4%A2%FF%26t