notmuch-dump: use fsync instead of fdatasync

Since the file size will have changed, there is no performance benefit
to calling fdatasync.  Somewhat surprisingly, using fdatasync
apparently causes portability problems on FreeBSD.
test/Makefile.local: Added configured TALLOC_LDFLAGS.

The linking to talloc is hard-coded in the testing Makefile. This patch
causes the linking to talloc to be done according to how TALLOC_LDFLAGS
was configured.

Signed-off-by: Charles Celerier <cceleri@cs.stanford.edu>
test: allow pending break points in atomicity script.

This seems to fix problems with the symbol rename not being defined
at startup on at least OS/X and some Debian Linux architectures.