Merge branch 'bc/parse-options-exit-0-on-help'

Merge branch 'bc/parse-options-exit-0-on-help'

Option parsing with 'git rev-parse --parseopt' and in most 'git'
subcommands has been updated to exit with 0 (instead of 129) when the
help option ('-h' or '--help') is requested directly by the user,
aligning with standard Unix convention.

* bc/parse-options-exit-0-on-help:
  parse-options: exit 0 on -h
  rev-parse: have --parseopt callers exit 0 on --help
  parse-options: add a separate case for help output on error
  t1517: skip svn tests if svn is not installed