t4041, t4205, t6006, t7102: Don't hardcode tested encoding value

The tested encoding is always available in a variable. Use it instead of
hardcoding. Also, to be in line with other tests use ISO8859-1
(uppercase) rather then iso8859-1.

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>
t4205 (log-pretty-format): Use `tformat` rather than `format`

Use `tformat` to avoid using of `echo` to complete end of line.

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>
t4205, t6006: Add failing tests for the case when i18n.logOutputEncoding is set

Pretty format string %<(N,[ml]trunc)>%s truncates subject to a given
length with an appropriate padding. This works for non-ASCII texts when
i18n.logOutputEncoding is UTF-8 only (independently of a printed commit
message encoding) but does not work when i18n.logOutputEncoding is NOT
UTF-8.

There were no breakages as far as were no tests for the case
when both a commit message and logOutputEncoding are not UTF-8.

Add failing tests for that which will be fixed in the next patch.

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>
Reviewed-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Reviewed-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
pretty.c: format string with truncate respects logOutputEncoding

Pretty format string %<(N,[ml]trunc)>%s truncates subject to a given
length with an appropriate padding. This works for non-ASCII texts when
i18n.logOutputEncoding is UTF-8 only (independently of a printed commit
message encoding) but does not work when i18n.logOutputEncoding is NOT
UTF-8.

In 7e77df3 (pretty: two phase conversion for non utf-8 commits, 2013-04-19)
'format_commit_item' function assumes commit message to be in UTF-8.
And that was so until ecaee80 (pretty: --format output should honor
logOutputEncoding, 2013-06-26) where conversion to logOutputEncoding was
added before calling 'format_commit_message'.

Correct this by converting a commit message to UTF-8 first (as it
assumed in 7e77df3 (pretty: two phase conversion for non utf-8 commits,
2013-04-19)). Only after that convert a commit message to an actual
logOutputEncoding.

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>
Reviewed-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>