convert elog(LOG) calls to ereport

There are a number of elog(LOG) calls that appear to be user-facing, so 
they should be ereport()s.  This patch changes them.  There are more 
elog(LOG) calls remaining, but they all appear to be some kind of 
debugging support.  Also, I changed a few elog(FATAL)s that were nearby, 
but I didn't specifically look for them.