(gzencode(string data [, int level [, int encoding_mode]])),
should fix#15930.
@- The second parameter of gzencode() now is the compression level like
@ in the documentation. The encoding mode is a third (optional) parameter.
# Rework of gzencode(), output should be closer to real gzip output.
# I think in the old version there could be some problems with
# this function and output compression, should be fixed, too.