make-check fails if not installed

[Alex Aycinena]

On a new clone on master, make-check fails on its first run (before being
installed) but succeeds after the application has been installed in its
install directory. This is because the guile symbol
'qof_backend_register_provider' is being looked for in three instances in
the install directory instead of in the build directory. The following is
reported in src/engine/test/test-suite.log:

FAIL: test-test-extras
======================

/home/gnucash-dev/gitcheckouts/gnucash-working-build/gnc-guile: symbol
lookup error:
/opt/gnucash-git/gnucash-working/lib/gnucash/libgncmod-backend-dbi.so:
undefined symbol: qof_backend_register_provider
FAIL test-test-extras (exit status: 127)

FAIL: test-account
==================

/home/gnucash-dev/gitcheckouts/gnucash-working-build/gnc-guile: symbol
lookup error:
/opt/gnucash-git/gnucash-working/lib/gnucash/libgncmod-backend-dbi.so:
undefined symbol: qof_backend_register_provider
FAIL test-account (exit status: 127)

FAIL: test-split
================

/home/gnucash-dev/gitcheckouts/gnucash-working-build/gnc-guile: symbol
lookup error:
/opt/gnucash-git/gnucash-working/lib/gnucash/libgncmod-backend-dbi.so:
undefined symbol: qof_backend_register_provider
FAIL test-split (exit status: 127)

Regards,

Alex