makemessages crashes with unicode filename and verbose > 1

[Arthur Koziel]

Running makemessages with a verbose level of >1 crashes with a UnicodeDecodeError when using a filename with unicode chars in it.

Steps to reproduce:

1. Create file with unicode chars in it (e.g. "200x200-åäöåäöåäöåäö.png")
2. Run "makemessages -v2"

Result: "UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 8: ordinal not in range(128)"
Expected: Command should skip file and print "UnicodeDecodeError: skipped file %s in %s" to stdout

[Claude Paroz]

I can reproduce. Passing unicode to os.walk should solve the issue. However, I'm not very comfortable adding non-ascii file names in the Django tree to test that issue.

[Claude Paroz <claude@…>]

In dbb48d2bb99a5f660cf2d85f137b8d87fc12d99f:

Applied unicode_literals to makemessages command

This also fixes #22686 as some sort of side-effect.

[Claude Paroz <claude@…>]

In cdfefbec721b59695e28e5992eda1cc52af48212:

[1.7.x] Applied unicode_literals to makemessages command

This also fixes #22686 as some sort of side-effect.
Backport of dbb48d2bb99 from master.

[Claude Paroz <claude@…>]

In 67870137b9e1f1384af7465b4eb978d0f4dab3b7:

[1.7.x] Fixed #22686 -- Prevented makemessages crash with unicode filename

A more extensive fix has been reverted on the 1.7.x branch, so this
minimal fix replaces it.