chainlint.pl: don't require `return|exit|continue` to end with `&&`

In order to check for &&-chain breakage, each time TestParser encounters a new command, it checks whether the previous command ends with `&&`, and -- with a couple exceptions -- signals breakage if it does not. The first exception is that a command may validly end with `||`, which is commonly employed as `command || return 1` at the very end of a loop body to terminate the loop early. The second is that piping one command's output with `|` to another command does not constitute a &&-chain break (the exit status of the pipe is the exit status of the final command in the pipe). However, it turns out that there are a few additional cases found in the wild in which it is likely safe for `&&` to be missing even when other commands follow. For instance: while {condition-1} do test {condition-2} || return 1 # or `exit 1` within a subshell more-commands done while {condition-1} do test {condition-2} || continue more-commands done Such cases indicate deliberate thought about failure modes by the test author, thus flagging them as breaking the &&-chain is not helpful. Therefore, take these special cases into consideration when checking for &&-chain breakage. Signed-off-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>