gnucash maint: Make backend sync errors survive to the session.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/3ccaec6e (commit)
	from  https://github.com/Gnucash/gnucash/commit/d2798b8c (commit)



commit 3ccaec6e381843b5e7f5ac03f199fc27fb9de2a4
Author: John Ralls <jralls at ceridwen.us>
Date:   Mon Jul 27 15:59:12 2015 -0700

    Make backend sync errors survive to the session.
    
    The backends were using qof_backend_get_error() to test for sync errors.
    This function clears the error, so the tests resulted in the error being
    cleared before the session could see it and so it thought that the sync
    had succeeded.
    
    Replace those uses of qof_backend_get_error() with a new function
    qof_backend_check_error() that doesn't clear the error.



Summary of changes:
 src/backend/dbi/gnc-backend-dbi.c |  2 +-
 src/backend/sql/gnc-backend-sql.c |  3 ++-
 src/backend/xml/io-gncxml-v2.c    | 20 +++++++++-----------
 src/libqof/qof/qofbackend.c       |  7 +++++++
 src/libqof/qof/qofbackend.h       |  8 ++++++++
 5 files changed, 27 insertions(+), 13 deletions(-)