Use appendStringInfoString() where appropriate in elog.c.
Use appendStringInfoString() where appropriate in elog.c.

The nominally equivalent call appendStringInfo(buf, "%s", str) can be
significantly slower when str is large.  In particular, the former usage in
EVALUATE_MESSAGE led to O(N^2) behavior when collecting a large number of
context lines, as I found out while testing recursive functions.  The other
changes are just neatnik-ism and seem unlikely to save anything meaningful,
but a cycle shaved is a cycle earned.

snaga/postgres-xl,Postgres-XL/Postgres-XL,jmcatamney/gpdb,oberstet/postgres-xl,ashwinstar/gpdb,arcivanov/postgres-xl,snaga/postgres-xl,xinzweb/gpdb,pavanvd/postgres-xl,Postgres-XL/Postgres-XL,50wu/gpdb,xinzweb/gpdb,yazun/postgres-xl,greenplum-db/gpdb,ovr/postgres-xl,zeroae/postgres-xl,adam8157/gpdb,tpostgres-projects/tPostgres,ovr/postgres-xl,snaga/postgres-xl,zeroae/postgres-xl,ashwinstar/gpdb,lisakowen/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,oberstet/postgres-xl,snaga/postgres-xl,techdragon/Postgres-XL,xinzweb/gpdb,snaga/postgres-xl,50wu/gpdb,adam8157/gpdb,ashwinstar/gpdb,Postgres-XL/Postgres-XL,oberstet/postgres-xl,ovr/postgres-xl,xinzweb/gpdb,adam8157/gpdb,tpostgres-projects/tPostgres,adam8157/gpdb,kmjungersen/PostgresXL,postmind-net/postgres-xl,lisakowen/gpdb,postmind-net/postgres-xl,greenplum-db/gpdb,kmjungersen/PostgresXL,lisakowen/gpdb,arcivanov/postgres-xl,Postgres-XL/Postgres-XL,xinzweb/gpdb,arcivanov/postgres-xl,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,yazun/postgres-xl,oberstet/postgres-xl,jmcatamney/gpdb,adam8157/gpdb,yazun/postgres-xl,techdragon/Postgres-XL,pavanvd/postgres-xl,Postgres-XL/Postgres-XL,greenplum-db/gpdb,greenplum-db/gpdb,xinzweb/gpdb,jmcatamney/gpdb,yazun/postgres-xl,kmjungersen/PostgresXL,pavanvd/postgres-xl,kmjungersen/PostgresXL,oberstet/postgres-xl,50wu/gpdb,techdragon/Postgres-XL,ashwinstar/gpdb,postmind-net/postgres-xl,zeroae/postgres-xl,50wu/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,lisakowen/gpdb,arcivanov/postgres-xl,tpostgres-projects/tPostgres,zeroae/postgres-xl,lisakowen/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,arcivanov/postgres-xl,postmind-net/postgres-xl,techdragon/Postgres-XL,postmind-net/postgres-xl,lisakowen/gpdb,adam8157/gpdb,techdragon/Postgres-XL,zeroae/postgres-xl,arcivanov/postgres-xl,lisakowen/gpdb,lisakowen/gpdb,ashwinstar/gpdb,yazun/postgres-xl,adam8157/gpdb,ovr/postgres-xl,ashwinstar/gpdb,tpostgres-projects/tPostgres,greenplum-db/gpdb,50wu/gpdb,tpostgres-projects/tPostgres,ashwinstar/gpdb,50wu/gpdb,kmjungersen/PostgresXL,pavanvd/postgres-xl,ovr/postgres-xl,greenplum-db/gpdb,ashwinstar/gpdb