[r23174]Bug #674862 - 2038 bug in libdbi

Retrieve the numerical value directly from the dbi_result and use
it to create the Timespec or GDate.

NB: In Gnucash 2.4 there are plenty of other 2038 bugs due to reliance
on the libc time functions. This has been corrected in trunk.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/branches/2.4@23177 57a11ea4-9604-0410-9ed3-97b8803252fd