tests: remove use of bashism $RANDOM to fix test-narrow.t on non-bash shells
This test passed on our workstations, including on Macs, so we never
noticed, but it fails on both the Linux and FreeBSD buildbots. Today I
learned about a bash feature, wherein $RANDOM gives a random int every
time you read it.
check-code rule to follow.
Differential Revision: https://phab.mercurial-scm.org/D2236
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1