reflect: crash TestGCBits in runGCProg

[aclements]

The earliest instance seems to be: http://build.golang.org/log/ebef81c8288d8fe5e9a4f4da70aafd9ede59f1b2 (2015-06-26T17:26:09-e0e47e2/freebsd-amd64-race). The crash isn't reliable, but it has happened frequently enough since that commit to implicate that commit or something very close to it. So far, all of the failures have been on amd64, but just about every OS.

This may also sometimes manifest as a test failure without a crash: http://build.golang.org/log/67be43ca33d74ef696b29b35e8d94d5ce256bddc (2015-06-26T17:49:33-32fddad/freebsd-amd64-gce101)

[aclements]

The crash isn't reliable, but it has happened frequently enough since that commit to implicate that commit or something very close to it.

The specific test line that's causing the crash was added by the commit just before e0e47e2 (4b28755), so that's why it started around here. The underlying bug presumably existed before.