quote: add sq_append_quote_argv_pretty()

quote: add sq_append_quote_argv_pretty()

sq_quote_argv_pretty() builds a "pretty" string from the given argv.
It inserts whitespace before each value, rather than just between
them, so the resulting string always has a leading space.  Lets give
callers an option to not have the leading space or have to ltrim()
it later.

Create sq_append_quote_argv_pretty() to convert an argv into a
pretty, quoted if necessary, string with space delimiters and
without a leading space.

Convert the existing sq_quote_argv_pretty() to use this new routine
while preserving the leading space behavior.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>