gnucash maint: Multiple changes pushed

[Christopher Lam]

Updated	 via  https://github.com/Gnucash/gnucash/commit/496ca94a (commit)
	 via  https://github.com/Gnucash/gnucash/commit/f72df3e1 (commit)
	 via  https://github.com/Gnucash/gnucash/commit/7587c3b4 (commit)
	 via  https://github.com/Gnucash/gnucash/commit/0511ce72 (commit)
	from  https://github.com/Gnucash/gnucash/commit/7a662272 (commit)



commit 496ca94a989d0001a64c19f5e2104ae02fe1a604
Author: Christopher Lam <christopher.lck at gmail.com>
Date:   Fri Sep 20 22:43:00 2019 +0800

    [reports] use new API gnc:collector+ and gnc:collector-

commit f72df3e1bc70b29ca74b12497044f093cc737fbe
Author: Christopher Lam <christopher.lck at gmail.com>
Date:   Sat Sep 21 13:49:34 2019 +0800

    [report-utilities] gnc:account-get-balances-at-dates: use quicksort
    
    stable-sort! is slower than quicksort.

commit 7587c3b4e337e513a4fb68f4b98bb26740e0f8c2
Author: Christopher Lam <christopher.lck at gmail.com>
Date:   Fri Sep 20 22:42:43 2019 +0800

    [API] gnc:collector+ and gnc:collector- for collector arithmetic
    
    (gnc:collector+ ...) equivalent to (+ ...)
    (gnc:collector- ...) equivalent to (- ...) and will also handle
    single-argument sign negation.

commit 0511ce723ee2ee52a9a5992bced6505577029e17
Author: Christopher Lam <christopher.lck at gmail.com>
Date:   Fri Sep 20 22:17:44 2019 +0800

    [API] gnc:list-flatten flattens lists recursively
    
    and is a schemey algorithm rather than a report algorithm, so, belongs
    centrally.



Summary of changes:
 .../report/business-reports/customer-summary.scm   | 17 +++++------
 gnucash/report/report-system/report-system.scm     |  2 ++
 gnucash/report/report-system/report-utilities.scm  | 21 ++++++++++++-
 .../report-system/test/test-report-utilities.scm   | 15 ++++++++++
 gnucash/report/standard-reports/balsheet-pnl.scm   |  5 ++--
 gnucash/report/standard-reports/budget.scm         | 13 +-------
 .../report/standard-reports/category-barchart.scm  | 10 ++-----
 gnucash/report/standard-reports/net-charts.scm     |  8 +----
 gnucash/report/standard-reports/trial-balance.scm  | 35 ++++++++--------------
 .../scm/test/test-libgnucash-scm-utilities.scm     | 12 ++++++++
 libgnucash/scm/utilities.scm                       | 12 ++++++++
 11 files changed, 86 insertions(+), 64 deletions(-)