[GNC] Custom reports don't survive upgrade to v3

[Macho Philipovich]

Dear gnucash users,

I decided to upgrade from the long-term support version of Ubuntu to the
current stable version this weekend.

This change, I would later learn, entailed upgrading gnucash from
v2.6.19 to v3.4.

The upgrade went fine, except that none of my four or five custom
reports work any more.

They mostly don't give any helpful error information but just show:

    *Report error*
    An error occurred while running the report.

One of the reports does, however, give some sort of stack trace, though
it's not terribly instructive either.

It's been quite a while since I've looked at any of this, so revisions
currently feel a bit daunting, but I do rely significantly on these
custom reports.

If anyone could point me to any resources on the changes to the reports
API since v2 and to any debugging resources, it would also be greatly
appreciated.

The reports are my own creations, except that one is an extremely
helpful year-to-date budget report that Phil Longstaff (in cc) provided
me some time ago over this list in a file he called ytd-budget.scm.
Phil, if by chance you've revised your report, I'd greatly appreciate a
copy. And I would very much +1 this report becoming part of the standard
reports provided within gnucash.

Many thanks,

Macho