Adjust tests for Imlib2 1.6+ ("jpeg" format is now "jpg")

test/feh.t

test/list_imlib2_1.6/custom

test/list_imlib2_1.6/default

test/list_imlib2_1.6/filename

test/list_imlib2_1.6/filename_recursive

test/list_imlib2_1.6/format

test/list_imlib2_1.6/format_reverse

test/list_imlib2_1.6/height

test/list_imlib2_1.6/name

test/list_imlib2_1.6/pixels

test/list_imlib2_1.6/size

test/list_imlib2_1.6/width