Mem allocation cleanup in command/verify module.

Move the temp mem context out of verifyJobCallback() into verifyBackup() and verifyArchive(). This makes it clearer that verifyJobCallback() allocates no memory and reduces mem usage when both verifyBackup() and verifyArchive() are called.

Update verifyErrorMsg() to return zero-terminated strings to save on allocations. The output of this function is used when formatting strings so this is also simpler. Do a similar thing in verifyRender().

Also fix a minor leak in verifyInfoFile().