Merge branch 'nd/diff-parseopt'

The diff machinery, one of the oldest parts of the system, which
long predates the parse-options API, uses fairly long and complex
handcrafted option parser.  This is being rewritten to use the
parse-options API.

* nd/diff-parseopt:
diff.c: convert --raw
diff.c: convert -W|--[no-]function-context
diff.c: convert -U|--unified
diff.c: convert -u|-p|--patch
diff.c: prepare to use parse_options() for parsing
diff.h: avoid bit fields in struct diff_flags
diff.h: keep forward struct declarations sorted
parse-options: allow ll_callback with OPTION_CALLBACK
parse-options: avoid magic return codes
parse-options: stop abusing 'callback' for lowlevel callbacks
parse-options: add OPT_BITOP()
parse-options: disable option abbreviation with PARSE_OPT_KEEP_UNKNOWN
parse-options: add one-shot mode
parse-options.h: remove extern on function prototypes

diff --cc Documentation/diff-options.txt
Simple merge

diff --cc builtin/blame.c
Simple merge

diff --cc builtin/merge.c
Simple merge

diff --cc builtin/update-index.c
Simple merge

diff --cc diff.c
Simple merge