The attached patch resolves a couple of problems with the current RTSP support.
It also adds a couple of features to make it possible to use the RTSP code in an RTSP server. Below is a suggested commit message, outlining the changes.

* gst/rtsp/rtspconnection.c: (rtsp_connection_create):
Allow url to be NULL to be able to use it for server connections.
* gst/rtsp/rtspconnection.c: (rtsp_connection_connect):
Require that conn->url is non-NULL.
* gst/rtsp/rtspconnection.c: (rtsp_connection_send):
Can now send responses as well as requests.
* gst/rtsp/rtspconnection.c: (read_line):
No longer hangs in an endless loop if EOF is received.
* gst/rtsp/rtspdefs.c: (rtsp_init_status), (rtsp_status_as_text):
Can now convert a status code to a text string.
* gst/rtsp/rtspdefs.c: (rtsp_status_to_string):
Removed.
* gst/rtsp/rtspdefs.c: (rtsp_find_header_field):
Return RTSP_HDR_INVALID for unknown headers.
* gst/rtsp/rtspdefs.c: (rtsp_find_method):
Return RTSP_INVALID for unknown methods.
* gst/rtsp/rtspmessage.c: (rtsp_message_new):
Create an empty message.
* gst/rtsp/rtspmessage.c: (rtsp_message_init):
Intialize an empty message.
* gst/rtsp/rtspmessage.c: (rtsp_message_new_response),
(rtsp_message_init_response):
Allow reason to be NULL, in which case rtsp_status_as_text() is
used to find the reason to use.
* gst/rtsp/rtspmessage.c: (rtsp_message_init_response):
Copy CSeq and Session headers from the request.
* gst/rtsp/rtspmessage.c: (rtsp_message_unset):
Only free memory corresponding to the currently set message type.
* gst/rtsp/rtspmessage.c: (rtsp_message_get_header):
Allow value to be NULL, to allow for checking the existence of a
header without retrieving it.
* gst/rtsp/rtspmessage.c: (rtsp_message_new_request),
(rtsp_message_init_request), (rtsp_message_new_response),
(rtsp_message_init_response), (rtsp_message_add_header),
(rtsp_message_get_header), (rtsp_message_set_body),
(rtsp_message_get_body):
* gst/rtsp/rtspmessage.h:
Added const to function arguments as appropriate.
* gst/rtsp/rtspconnection.c: (read_line), (rtsp_connection_read):
* gst/rtsp/rtspmessage.c: (dump_mem):
* gst/rtsp/sdpmessage.c: (sdp_message_get_attribute_val_n),
(sdp_media_get_attribute_val_n), (read_string), (read_string_del),
(sdp_message_parse_buffer), (print_media), (sdp_message_dump):
Use guint rather than gint to avoid compiler warnings.
* gst/rtsp/sdpmessage.c: (sdp_parse_line):
Avoid a compiler warning when initializing nmedia.