Merge branch 'jk/string-list-static-init'

Merge branch 'jk/string-list-static-init'

Instead of taking advantage of a struct string_list that is
allocated with all NULs happens to be STRING_LIST_INIT_NODUP kind,
initialize them explicitly as such, to document their behaviour
better.

* jk/string-list-static-init:
  use string_list initializer consistently
  blame,shortlog: don't make local option variables static
  interpret-trailers: don't duplicate option strings
  parse_opt_string_list: stop allocating new strings