Background indexing is ok, forground inding crashes.

Tue Dec 20 14:48:40 [conn2] build index test.huge_multikey_index

Tue Dec 20 14:48:45 [conn2] couldn't open /data/db/sconsTests/_tmp/esort.1324410520.1552787748//file.1010 errno:24 Too many open files
Tue Dec 20 14:48:45 [conn2] Assertion: 10308:mmap failed
0x5b01f0 0x5b2a0e 0x8731db 0x873418 0x8580cd 0x84d3fd 0x84e1b0 0x84f9ae 0x85062e 0x82f6a0 0x831c8a 0x83600b 0x836842 0x96e0c8 0x6371f9 0x7f5eaf522df0 0x7f5eae2292ed
/home/mstearn/10gen/mongo/mongod() [0x5b01f0]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo11msgassertedEiPKc+0xbe) [0x5b2a0e]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo21BSONObjExternalSorter12FileIteratorC1ESs+0xab) [0x8731db]
/home/mstearn/10gen/mongo/mongod(ZN5mongo21BSONObjExternalSorter8IteratorC1EPS0+0x1f8) [0x873418]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo24buildBottomUpPhases2And3INS_12BtreeData_V1EEEvbRNS_12IndexDetailsERNS_21BSONObjExternalSorterEbRSt4listINS_7DiskLocESaIS7_EEPNS_5CurOpEPNS_12SortPhaseOneERNS_19ProgressMeterHolderERNS_5TimerE+0x7d) [0x8580cd]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo14fastBuildIndexEPKcPNS_16NamespaceDetailsERNS_12IndexDetailsEi+0x60d) [0x84d3fd]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo16insert_makeIndexEPNS_16NamespaceDetailsERKSsRKNS_7DiskLocE+0x360) [0x84e1b0]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo11DataFileMgr6insertEPKcPKvibbPb+0x30e) [0x84f9ae]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo11DataFileMgr16insertWithObjModEPKcRNS_7BSONObjEb+0x3e) [0x85062e]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo14checkAndInsertEPKcRNS_7BSONObjE+0xb0) [0x82f6a0]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo14receivedInsertERNS_7MessageERNS_5CurOpE+0x25a) [0x831c8a]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo17_assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE+0x171b) [0x83600b]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE+0x32) [0x836842]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo16MyMessageHandler7processERNS_7MessageEPNS_21AbstractMessagingPortEPNS_9LastErrorE+0x88) [0x96e0c8]
/home/mstearn/10gen/mongo/mongod(_ZN5mongo3pms9threadRunEPNS_13MessagingPortE+0x289) [0x6371f9]
/lib/libpthread.so.0(+0x7df0) [0x7f5eaf522df0]
/lib/libc.so.6(clone+0x6d) [0x7f5eae2292ed]
Tue Dec 20 14:48:45 terminate() called, printing stack:
...

slowNightly test will be committed shortly

Fails with 1.8, 2.0, and master.