Revert "Fix broken test-backend-dbi with libdbi 0.9."

This reverts commit 321a159af29a9b51fe793c2528dccb74b0443bf9.
Got two unrelated changes into a single changeset.
Add note about automake 1.14 to configure.ac

The note has the details, but I wasn't able to get gnucash to build with
automake 1.14 without passing --disable-dependency-tracking regardless of
whether I used the subdir-objects option. If I could figure out a good way
to poison configure with automake 1.14 I would.
Fix uninitialized variable warning.
Fix test-backend-dbi segfault with libdbi-0.9.0.

dbi_inst must be initialized before it can be used.