Merge branch 'sb/range-diff-colors'

The color output support for recently introduced "range-diff"
command got tweaked a bit.

* sb/range-diff-colors:
range-diff: indent special lines as context
range-diff: make use of different output indicators
diff.c: add --output-indicator-{new, old, context}
diff.c: rewrite emit_line_0 more understandably
diff.c: omit check for line prefix in emit_line_0
diff: use emit_line_0 once per line
diff.c: add set_sign to emit_line_0
diff.c: reorder arguments for emit_line_ws_markup
diff.c: simplify caller of emit_line_0
t3206: add color test for range-diff --dual-color
test_decode_color: understand FAINT and ITALIC

diff --cc diff.c
Simple merge

diff --cc diff.h
Simple merge

diff --cc t/test-lib-functions.sh
Simple merge