Made several functions static
Made one function defined to nothing when RTSP is disabled to avoid
the #ifdefs in code.
Removed explicit rtsp.h includes
The RTSP-specific function for checking for "dead" connection is better
located in rtsp.c. The code using this is now written without #ifdefs as
the function call is instead turned into a macro (in rtsp.h) when RTSP
is disabled.
It helps to prevent a hangup with some FTP servers in case idle session
timeout has exceeded. But it may be useful also for other protocols
that send any quit message on disconnect. Currently used by FTP, POP3,
IMAP and SMTP.
