gnucash maint: gnc:get-commodity-totalavg-prices shouldn't use 0-amount splits.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/6dfbf3d5 (commit)
	from  https://github.com/Gnucash/gnucash/commit/c977c235 (commit)



commit 6dfbf3d5e7bed8e09c650b994e62ff74715bdfc9
Author: John Ralls <jralls at ceridwen.us>
Date:   Thu Aug 30 11:02:16 2018 -0700

    gnc:get-commodity-totalavg-prices shouldn't use 0-amount splits.
    
    get-commodity-totalavg-prices seeks to create a share-weighted average of
    all prices for a commodity and 0-share splits (normally used to book
    trading gains) don't represent a price and so distort (sometimes
    dramatically) the resulting average as well as creating extra invalid
    entries in the resulting alist.



Summary of changes:
 .../report/report-system/commodity-utilities.scm   | 87 ++++++++++++----------
 .../report-system/test/test-commodity-utils.scm    |  6 +-
 2 files changed, 52 insertions(+), 41 deletions(-)