Improve documentation of psql's \q command.
Improve documentation of psql's \q command.

The documentation neglected to explain its behavior in a script file
(it only ends execution of the script, not psql as a whole), and failed
to mention the long form \quit either.

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