4813885: RFE: GZIPOutputStream should implement flush using Z_SYNC_FLUSH

[Xueming Shen]

Martin,

Would you please help review the change for

4813885: RFE: GZIPOutputStream should implement flush using Z_SYNC_FLUSH

http://cr.openjdk.java.net/~sherman/4813885/webrev

It appears people want to have the same flush option in GZIPOutputStream 
as the
one we provided in DeflaterOutputStream for #4206909 a while ago, the 
webrev for
4206909 is at

http://cr.openjdk.java.net/~sherman/4206909/webrev

Thanks,
-Sherman