gnucash maint: Simplify gnc_commodity equality and compare functions.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/46f9fb01 (commit)
	from  https://github.com/Gnucash/gnucash/commit/a81b72f0 (commit)



commit 46f9fb01c972615ff77152f0c76489d761925e15
Author: John Ralls <jralls at ceridwen.us>
Date:   Tue Jan 24 09:46:48 2023 -0800

    Simplify gnc_commodity equality and compare functions.
    
    gnc_commodity_compare is used for sorting and so needs to have a less-than
    return value. The only place it's used presents nothing to the UI; a GncGUID
    ordering is fast and stable.
    
    GnuCash allows only one commodity per book for any namespace/mnemonic pair, so
    the exhaustive string comparisons are superflous. While the current engine
    design allows only one instance of any object, meaning that a pointer comparison
    is sufficient to determine equality, that may not be true in the future, but the
    GncGUID is guaranteed to sufficiently identify a single commodity. Note that
    gnc_commodity_equiv is used to enforce that single-commodity rule and so cannot
    use GncGUID comparison.



Summary of changes:
 libgnucash/engine/gnc-commodity.c | 71 +++++++--------------------------------
 1 file changed, 12 insertions(+), 59 deletions(-)