Assertion failure in base backup code path

In HEAD, pg_basebackup causes WAL sender to fail when the replication
user is not a superuser:

#0 0x00007f34f671dd25 in raise () from /lib64/libc.so.6
#1 0x00007f34f671f1a8 in abort () from /lib64/libc.so.6
#2 0x00000000008989a9 in ExceptionalCondition (conditionName=0xa51ac1
"!(IsTransactionState())", errorType=0xa51734 "FailedAssertion",
fileName=0xa516e0 "catcache.c", lineNumber=1111) at assert.c:54
#3 0x000000000087ea36 in SearchCatCache (cache=0x23c4fb8, v1=16384,
v2=0, v3=0, v4=0) at catcache.c:1111
#4 0x0000000000890cdd in SearchSysCache (cacheId=11, key1=16384,
key2=0, key3=0, key4=0) at syscache.c:909
#5 0x00000000008a9a99 in has_rolreplication (roleid=16384) at
miscinit.c:401
#6 0x00000000005146d1 in do_pg_start_backup (backupidstr=0x239d5b0
"bkp_01", fast=0 '\000', starttli_p=0x7fff78e4f8ec,
labelfile=0x7fff78e4f8e0) at xlog.c:9633
#7 0x0000000000733a24 in perform_base_backup (opt=0x7fff78e4fa30,
tblspcdir=0x242c6a0) at basebackup.c:106
#8 0x0000000000735013 in SendBaseBackup (cmd=0x239dbf8) at basebackup.c:563
#9 0x000000000072f4f2 in exec_replication_command (cmd_string=0x23ea078
"BASE_BACKUP LABEL 'bkp_01' WAL NOWAIT") at walsender.c:668
#10 0x000000000077c5c4 in PostgresMain (argc=1, argv=0x2385358,
dbname=0x2385248 "", username=0x2385210 "postgres_replication") at
postgres.c:4009
#11 0x0000000000717c94 in BackendRun (port=0x23a2e90) at postmaster.c:4085
#12 0x000000000071742e in BackendStartup (port=0x23a2e90) at
postmaster.c:3774
#13 0x0000000000713cc9 in ServerLoop () at postmaster.c:1585
#14 0x0000000000713370 in PostmasterMain (argc=3, argv=0x2381f60) at
postmaster.c:1240
#15 0x0000000000677698 in main (argc=3, argv=0x2381f60) at main.c:196

Some additional condition may be needed in the Assert() statement?

// Antonin Houska (Tony)