"git blame -L :funcname -- path" did not work well for a path for
which a userdiff driver is defined.
* pb/blame-funcname-range-userdiff:
blame: simplify 'setup_blame_bloom_data' interface
blame: simplify 'setup_scoreboard' interface
blame: enable funcname blaming with userdiff driver
line-log: mention both modes in 'blame' and 'log' short help
doc: add more pointers to gitattributes(5) for userdiff
blame-options.txt: also mention 'funcname' in '-L' description
doc: line-range: improve formatting
doc: log, gitk: move '-L' description to 'line-range-options.txt'