config: push path() into moveifchanged()

[kevans]

Summary

Every caller path()s its arguments anyways, just simplify these and push
path() into moveifchanged(). This fixes a number of memory leaks since
path() allocates memory.

While we're here, make sure we close from_fd/to_fd appropriately and
have path() error out if the allocation fails.

CID: 1471040, 1471714, 1472045, 1505250, 1006907, 1006908

[imp]

These look good. I'd be half tempted to do the memory cleanup and fd leaks as separate commits, but it's not terrible if they wind up being one.

usr.sbin/config/main.cc

461

Good change, but not mentioned in commit log.

[emaste]

usr.sbin/config/main.cc

611

these error messages don't necessarily have to change (I have no opinion on which is better)

[kevans]

usr.sbin/config/main.cc

461

This was glossed over as "have path() error out if the allocation fails."