transactions: change backupfiles format to use newlines Previously the journal.backupfiles file was delimited by \0. Now we delimit it using \n (same as the journal file). This allows us to change the number of values in each line more easily, rather than relying on the count of \0's.

transactions: add version number to journal.backupfiles The transaction format will be changing a bit over the next releases, so let's go ahead and add a version number to make backwards compatibility easier. This whole file format was broken prior to 3.2 (see previous patch), so changing it now is pretty low risk.

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.