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Cleaned up stringhandling for binary safeness.
All functions now maintain a global 'errno' variable.
All functions now print warning messages on failure.
Added error code constants.
Fixed bug #8041 while maintaining backward compatibility.
New functions:
yp_all traverse a map
yp_cat retrive an entire map in one go
yp_errno get last error code
yp_err_string get a human readable error message
