transactions: fix hg recover with fncache backups
The transaction backupfiles logic was broken for 'hg recover'. The file format
is XXX\0XXX\0YYY\0YYY\0 but the parser did a couple things wrong. 1) It went one
step beyond the final \0 and tried to read past the end of the array. 2)
array[i:i+1] returns a single item, instead of two items as intended.
Added a test to catch it, which turns out to be the first actual 'hg recover'
test.
running: init test1
result: None
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: None
running: commit -m commit2 -d 2000-01-02 foo
result: None
running: log -r 0
changeset: 0:0e4634943879
user: test
date: Sat Jan 01 00:00:00 2000 +0000
summary: commit1
result: None
running: log -r tip
changeset: 1:45589e459b2e
tag: tip
user: test
date: Sun Jan 02 00:00:00 2000 +0000
summary: commit2
result: None