Minor code review for json.c.
Minor code review for json.c.

Improve commenting, conform to project style for use of ++ etc.
No functional changes.

(cherry-picked from f871ef74a5560377d541e6d94704f30bcbcdb779)

Author:             Álvaro Hernández Tortosa <f2a78ee48bb80ec86293791e21def221500feff0@8kdata.com>
Date:               Tue Jun 14 22:02:55 UTC 2016

yuanzhao/gpdb,cjcjameson/gpdb,xuegang/gpdb,xuegang/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,xuegang/gpdb,rvs/gpdb,cjcjameson/gpdb,ashwinstar/gpdb,edespino/gpdb,adam8157/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,lisakowen/gpdb,kaknikhil/gpdb,xuegang/gpdb,lintzc/gpdb,Chibin/gpdb,ashwinstar/gpdb,50wu/gpdb,kaknikhil/gpdb,0x0FFF/gpdb,Chibin/gpdb,Quikling/gpdb,rvs/gpdb,yuanzhao/gpdb,0x0FFF/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,kaknikhil/gpdb,0x0FFF/gpdb,lisakowen/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,royc1/gpdb,janebeckman/gpdb,0x0FFF/gpdb,Chibin/gpdb,Quikling/gpdb,lintzc/gpdb,lintzc/gpdb,janebeckman/gpdb,rvs/gpdb,Quikling/gpdb,edespino/gpdb,rvs/gpdb,cjcjameson/gpdb,adam8157/gpdb,royc1/gpdb,Chibin/gpdb,adam8157/gpdb,50wu/gpdb,janebeckman/gpdb,Chibin/gpdb,cjcjameson/gpdb,janebeckman/gpdb,xinzweb/gpdb,0x0FFF/gpdb,edespino/gpdb,yuanzhao/gpdb,CraigHarris/gpdb,xuegang/gpdb,CraigHarris/gpdb,cjcjameson/gpdb,kaknikhil/gpdb,edespino/gpdb,lisakowen/gpdb,lintzc/gpdb,kaknikhil/gpdb,xinzweb/gpdb,cjcjameson/gpdb,Quikling/gpdb,CraigHarris/gpdb,rvs/gpdb,lintzc/gpdb,lintzc/gpdb,yuanzhao/gpdb,adam8157/gpdb,CraigHarris/gpdb,lisakowen/gpdb,kaknikhil/gpdb,50wu/gpdb,adam8157/gpdb,Quikling/gpdb,edespino/gpdb,Quikling/gpdb,janebeckman/gpdb,xinzweb/gpdb,royc1/gpdb,janebeckman/gpdb,Chibin/gpdb,royc1/gpdb,royc1/gpdb,royc1/gpdb,Chibin/gpdb,Quikling/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,adam8157/gpdb,rvs/gpdb,50wu/gpdb,cjcjameson/gpdb,0x0FFF/gpdb,lisakowen/gpdb,rvs/gpdb,adam8157/gpdb,lintzc/gpdb,jmcatamney/gpdb,rvs/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,edespino/gpdb,50wu/gpdb,CraigHarris/gpdb,janebeckman/gpdb,greenplum-db/gpdb,lisakowen/gpdb,rvs/gpdb,janebeckman/gpdb,royc1/gpdb,50wu/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,cjcjameson/gpdb,janebeckman/gpdb,xinzweb/gpdb,kaknikhil/gpdb,edespino/gpdb,50wu/gpdb,xuegang/gpdb,jmcatamney/gpdb,Quikling/gpdb,jmcatamney/gpdb,Chibin/gpdb,adam8157/gpdb,Quikling/gpdb,lintzc/gpdb,greenplum-db/gpdb,CraigHarris/gpdb,greenplum-db/gpdb,xuegang/gpdb,50wu/gpdb,ashwinstar/gpdb,janebeckman/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,edespino/gpdb,edespino/gpdb,xinzweb/gpdb,xuegang/gpdb,CraigHarris/gpdb,lisakowen/gpdb,lintzc/gpdb,ashwinstar/gpdb,Quikling/gpdb,jmcatamney/gpdb,Chibin/gpdb,yuanzhao/gpdb,CraigHarris/gpdb,jmcatamney/gpdb,kaknikhil/gpdb,rvs/gpdb,yuanzhao/gpdb,0x0FFF/gpdb,CraigHarris/gpdb,cjcjameson/gpdb,Chibin/gpdb,xinzweb/gpdb,royc1/gpdb,yuanzhao/gpdb,xuegang/gpdb,edespino/gpdb,0x0FFF/gpdb