Merge branch 'rs/date-mode-pass-by-value'

The codepaths that reach date_mode_from_type() have been updated to
pass "struct date_mode" by value to make them thread safe.

* rs/date-mode-pass-by-value:
  date: make DATE_MODE thread-safe

diff --cc gpg-interface.c
Simple merge

diff --cc log-tree.c
Simple merge

diff --cc pretty.c
Simple merge

diff --cc pretty.h
Simple merge