psLogSetDestination is inconsistent

[Paul Price]

Some parts of the SDRS state:
Specifying a \code{format} of \code{NULL} turns off logging (equivalent
to calling \code{psLogSetDestination(PS_LOG_TO_NONE)}, whereas if the
\code{format} is \code{""}, then the format reverts to the default.

But the definition says:

bool psLogSetDestination(int fd);
If the \code{fd} is 0, then the log is sent to standard output,
otherwise it is sent to the specified file descriptor. A call to
\code{psLogSetDestination} automatically closes an open file
descriptor.

And the implementation has an enum, with PS_LOG_NONE = 0, which means that the
user thinks the logging is being turned on to stdout, but it's been disabled.

To fix this, I propose:

enum {

PS_LOG_TO_NONE = 0, /< turn off logging
PS_LOG_TO_STDOUT = 1, /< log to system's stdout
PS_LOG_TO_STDERR = 2, /< log to system's stderr

};

These values echo the file descriptor values for stdin, stdout and stderr,
repectively. I would argue that this makes the most sense.

I will fix the SDRS, if there are no objections.

[Paul Price]

Ditto for the trace messages.

[Paul Price]

Updated the SDRS. It'll be in the next release.