Patch taken from the upstream repository, should be fixed in next
released version.
This did require moving the invocation of `patchShebangs` from
`patchPhase` to `postpatch`, but this seems consistent with at least
some other packages.
My accounts are stored in the DBI backend (SQLite, specifically).
Before the present change, GnuCash would be compiled without DBI
support (`--disable-dbi` flag), so I could only use the XML backend.
Now I can use either backend.
I made the change only for 2.6. It looks like 2.4 works the same way,
so maybe I'll enable DBI for that one later.
Making nix packages is delightful! It might replace my accounting hobby!