1. osrfLogGetXid now returns a pointer to const. We don't want the

1. osrfLogGetXid now returns a pointer to const.  We don't want the
calling code to be able to overwrite the cached copy of the
transaction id.

2. Add doxygen-style comments to document some of the functions.

M    include/opensrf/log.h
M    src/libopensrf/log.c

git-svn-id: svn://svn.open-ils.org/OpenSRF/trunk@1811 9efc2488-bf62-4759-914b-345cdb29e865