Implemented session_connected(), which had been declared in the header but never

Implemented session_connected(), which had been declared in the header but never
defined.

Changed transport_client.c to use session_connected(), so that it wouldn't need to
see a declaration of jabber_machine.

Moved from transport_session.h to transport_session.c: several macros and the
declaration of jabber_machine, of which none are needed elsewhere.

Removed some comments from the header so that they won't override more complete
comments in the implementation file.

In session_connect(): inserted a return statement in order to bypass some
superfluous string comparisons.

Added the const qualifier to the return type of get_xml_attr().  We don't want to
be able to overwrite the text returned by the XML parser.

In endElementHandler(): look for "stream:error", to match the opening tag, instead
of "error:error".

Resest status_buffer along with the other buffers.

Introduced several minor performance tweaks.

Added more doxygen-style comments for documentation.

M    include/opensrf/transport_session.h
M    src/libopensrf/transport_session.c
M    src/libopensrf/transport_client.c

git-svn-id: svn://svn.open-ils.org/OpenSRF/trunk@1823 9efc2488-bf62-4759-914b-345cdb29e865