gitk: Catch mkdtemp errors

105b5d3f ("gitk: Use mktemp -d to avoid predictable temporary
directories") introduced a dependency on mkdtemp, which is not
available on Windows.

Use the original temporary directory behavior when mkdtemp fails.
This makes the code use mkdtemp when available and gracefully
fallback to the existing behavior when it is not available.

Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
gitk: Add visiblerefs option, which lists always-shown branches

When many branches contain a commit, the branches used to be shown in
the form "A, B and many more", where A, B can be master of current
HEAD. But there are more which might be interesting to always know about.
For example, "origin/master".

The new option, visiblerefs, is stored in ~/.gitk. It contains a list
of references which are always shown before "and many more" if they
contain the commit. By default it is `{"master"}', which is compatible
with previous behavior.

Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>
gitk: Add keybinding to switch to parent commit

Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>
gitk: Updated Bulgarian translation (302t,0f,0u)

Signed-off-by: Alexander Shopov <ash@kambanaria.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Merge remote-tracking branch 'ozlabs/master' into releases/SuHo