MFC r311572, r311895, r311928, r311985, r312395, r312417

r311572:
Fix file descriptor leaks in cmp(1)

Also, add a few test cases

Reported by: Coverity
CID: 271624 275338
Reviewed by: ngie
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D9074

r311895:
Fix memory leaks during "tail -r" of an irregular file

• Rewrite r_buf to use standard tail queues instead of a hand-rolled circular linked list. Free dynamic allocations when done.
• Remove an optimization for the case where the file is a multiple of 128KB in size and there is a scarcity of memory.
• Add ATF tests for "tail -r" and its variants.

Reported by: Valgrind
Reviewed by: ngie
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D9067

r311928:
Fix build of usr.bin/tail with GCC

Submitted by: pluknet
Reported by: pluknet
MFC after: 27 days
X-MFC-with: 311895
Sponsored by: Spectra Logic Corp

r311985:
Fix uninitialized variable CIDs in route6d

The variables in question are actually return arguments, but it's still good
form to initialize them.

Reported by: Coverity
CID: 979679 979680
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp

r312395:
Fix several Coverity CIDs in devd

CID 1362055, 1362054: File descriptor leaks during shutdown
CID 1362013: Potential null-termination fail with long network device names
CID 1362097: Uncaught exception during memory pressure
CID 1362017, 1362016: Unchecked errors, possibly resulting in weird behavior
if two devd instances start at the same time.
CID 1362015: Unchecked error that will probably never fail

Reported by: Coverity
CID: 1362055 1362054 1362013 1362097 1362017 1362016 1362015
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp

r312417:
Fix build of devd with GCC 4.2

Reported by: olivier
Pointy-hat-to: asomers
MFC after: 27 days
X-MFC-with: 312395
Sponsored by: Spectra Logic Corp