Hook up flock() compat code.

Also a couple of minor changes: fail if we can't lock instead of
silently succeeding, and apply a couple of minor style fixes.
diff --git a/configure.ac b/configure.ac
index a70d406..35e2e8d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1723,6 +1723,7 @@
 	explicit_bzero \
 	fchmod \
 	fchown \
+	flock \
 	freeaddrinfo \
 	freezero \
 	fstatfs \