Provide a more helpful error message when there is an autoconf version mismatch;  backpatch.
Provide a more helpful error message when there is an autoconf version
mismatch;  backpatch.

jmcatamney/gpdb,ashwinstar/gpdb,Postgres-XL/Postgres-XL,ahachete/gpdb,chrishajas/gpdb,xinzweb/gpdb,Chibin/gpdb,yazun/postgres-xl,Quikling/gpdb,tpostgres-projects/tPostgres,xuegang/gpdb,lintzc/gpdb,royc1/gpdb,yuanzhao/gpdb,yazun/postgres-xl,Postgres-XL/Postgres-XL,cjcjameson/gpdb,snaga/postgres-xl,cjcjameson/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,ovr/postgres-xl,greenplum-db/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,kmjungersen/PostgresXL,ovr/postgres-xl,arcivanov/postgres-xl,xinzweb/gpdb,Chibin/gpdb,kaknikhil/gpdb,CraigHarris/gpdb,yuanzhao/gpdb,CraigHarris/gpdb,kaknikhil/gpdb,royc1/gpdb,yazun/postgres-xl,CraigHarris/gpdb,Postgres-XL/Postgres-XL,lintzc/gpdb,zaksoup/gpdb,cjcjameson/gpdb,lintzc/gpdb,ovr/postgres-xl,oberstet/postgres-xl,Postgres-XL/Postgres-XL,CraigHarris/gpdb,xinzweb/gpdb,Quikling/gpdb,xinzweb/gpdb,zaksoup/gpdb,0x0FFF/gpdb,yuanzhao/gpdb,oberstet/postgres-xl,oberstet/postgres-xl,edespino/gpdb,jmcatamney/gpdb,0x0FFF/gpdb,adam8157/gpdb,ashwinstar/gpdb,Chibin/gpdb,oberstet/postgres-xl,adam8157/gpdb,pavanvd/postgres-xl,kmjungersen/PostgresXL,postmind-net/postgres-xl,zaksoup/gpdb,royc1/gpdb,tpostgres-projects/tPostgres,edespino/gpdb,Quikling/gpdb,xuegang/gpdb,Quikling/gpdb,ahachete/gpdb,kaknikhil/gpdb,zeroae/postgres-xl,50wu/gpdb,chrishajas/gpdb,ahachete/gpdb,royc1/gpdb,ashwinstar/gpdb,edespino/gpdb,snaga/postgres-xl,yazun/postgres-xl,Quikling/gpdb,rvs/gpdb,ahachete/gpdb,cjcjameson/gpdb,lintzc/gpdb,royc1/gpdb,pavanvd/postgres-xl,snaga/postgres-xl,Postgres-XL/Postgres-XL,janebeckman/gpdb,zaksoup/gpdb,postmind-net/postgres-xl,0x0FFF/gpdb,lintzc/gpdb,lisakowen/gpdb,Quikling/gpdb,CraigHarris/gpdb,ahachete/gpdb,xuegang/gpdb,greenplum-db/gpdb,chrishajas/gpdb,arcivanov/postgres-xl,Chibin/gpdb,zeroae/postgres-xl,0x0FFF/gpdb,Chibin/gpdb,zaksoup/gpdb,50wu/gpdb,yuanzhao/gpdb,janebeckman/gpdb,edespino/gpdb,chrishajas/gpdb,ashwinstar/gpdb,janebeckman/gpdb,kaknikhil/gpdb,rvs/gpdb,janebeckman/gpdb,cjcjameson/gpdb,techdragon/Postgres-XL,50wu/gpdb,postmind-net/postgres-xl,50wu/gpdb,cjcjameson/gpdb,tpostgres-projects/tPostgres,techdragon/Postgres-XL,lisakowen/gpdb,tpostgres-projects/tPostgres,lisakowen/gpdb,snaga/postgres-xl,jmcatamney/gpdb,Chibin/gpdb,snaga/postgres-xl,edespino/gpdb,Chibin/gpdb,zeroae/postgres-xl,ashwinstar/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,xuegang/gpdb,rvs/gpdb,yuanzhao/gpdb,0x0FFF/gpdb,Chibin/gpdb,ashwinstar/gpdb,janebeckman/gpdb,lisakowen/gpdb,janebeckman/gpdb,rvs/gpdb,rvs/gpdb,janebeckman/gpdb,adam8157/gpdb,zaksoup/gpdb,zeroae/postgres-xl,50wu/gpdb,arcivanov/postgres-xl,jmcatamney/gpdb,0x0FFF/gpdb,arcivanov/postgres-xl,janebeckman/gpdb,adam8157/gpdb,CraigHarris/gpdb,chrishajas/gpdb,cjcjameson/gpdb,edespino/gpdb,yuanzhao/gpdb,adam8157/gpdb,kmjungersen/PostgresXL,rvs/gpdb,lisakowen/gpdb,chrishajas/gpdb,edespino/gpdb,ahachete/gpdb,edespino/gpdb,arcivanov/postgres-xl,yazun/postgres-xl,cjcjameson/gpdb,postmind-net/postgres-xl,janebeckman/gpdb,xinzweb/gpdb,rvs/gpdb,0x0FFF/gpdb,adam8157/gpdb,adam8157/gpdb,xuegang/gpdb,kaknikhil/gpdb,lintzc/gpdb,chrishajas/gpdb,kmjungersen/PostgresXL,greenplum-db/gpdb,ovr/postgres-xl,cjcjameson/gpdb,edespino/gpdb,ahachete/gpdb,adam8157/gpdb,xuegang/gpdb,oberstet/postgres-xl,postmind-net/postgres-xl,xinzweb/gpdb,pavanvd/postgres-xl,royc1/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,kmjungersen/PostgresXL,Quikling/gpdb,greenplum-db/gpdb,Chibin/gpdb,yuanzhao/gpdb,lintzc/gpdb,ahachete/gpdb,greenplum-db/gpdb,Quikling/gpdb,kaknikhil/gpdb,Quikling/gpdb,edespino/gpdb,CraigHarris/gpdb,jmcatamney/gpdb,lintzc/gpdb,zaksoup/gpdb,lintzc/gpdb,ashwinstar/gpdb,zeroae/postgres-xl,CraigHarris/gpdb,xuegang/gpdb,lisakowen/gpdb,janebeckman/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,royc1/gpdb,greenplum-db/gpdb,rvs/gpdb,Quikling/gpdb,kaknikhil/gpdb,zaksoup/gpdb,arcivanov/postgres-xl,rvs/gpdb,kaknikhil/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,techdragon/Postgres-XL,chrishajas/gpdb,Chibin/gpdb,ashwinstar/gpdb,rvs/gpdb,pavanvd/postgres-xl,yuanzhao/gpdb,xuegang/gpdb,tpostgres-projects/tPostgres,ovr/postgres-xl,royc1/gpdb,xuegang/gpdb,CraigHarris/gpdb,techdragon/Postgres-XL,xinzweb/gpdb,0x0FFF/gpdb