golint -min_confidence=0.3 .

golint -min_confidence=0.3 .

This commits removes a number of golint warnings. There is a class of warnings which I can't fix due to insufficient knowledge of the domain at this point. These are listed here:
```
addrmanager.go:907:1: comment on exported method AddrManager.Attempt should be of the form "Attempt ..."
addrmanager.go:1048:1: exported function RFC1918 should have comment or be unexported
addrmanager.go:1058:1: exported function RFC3849 should have comment or be unexported
addrmanager.go:1065:1: exported function RFC3927 should have comment or be unexported
addrmanager.go:1073:1: exported function RFC3964 should have comment or be unexported
addrmanager.go:1081:1: exported function RFC4193 should have comment or be unexported
addrmanager.go:1089:1: exported function RFC4380 should have comment or be unexported
addrmanager.go:1097:1: exported function RFC4843 should have comment or be unexported
addrmanager.go:1105:1: exported function RFC4862 should have comment or be unexported
addrmanager.go:1113:1: exported function RFC6052 should have comment or be unexported
addrmanager.go:1121:1: exported function RFC6145 should have comment or be unexported
addrmanager.go:1128:1: exported function Tor should have comment or be unexported
addrmanager.go:1143:1: exported function Local should have comment or be unexported
addrmanager.go:1228:2: exported const InterfacePrio should have comment (or a comment on this block) or be unexported
discovery.go:26:2: exported var ErrTorInvalidAddressResponse should have comment or be unexported
limits/limits_unix.go:19:1: exported function SetLimits should have comment or be unexported
limits/limits_windows.go:7:1: exported function SetLimits should have comment or be unexported
util/dropafter/dropafter.go:22:6: exported type ShaHash should have comment or be unexported
util/dropafter/dropafter.go:38:2: exported const ArgSha should have comment (or a comment on this block) or be unexported
util/dropafter/dropafter.go:128:5: exported var ErrBadShaPrefix should have comment or be unexported
util/dropafter/dropafter.go:129:5: exported var ErrBadShaLen should have comment or be unexported
util/dropafter/dropafter.go:130:5: exported var ErrBadShaChar should have comment or be unexported
util/showblock/showblock.go:24:6: exported type ShaHash should have comment or be unexported
util/showblock/showblock.go:46:2: exported const ArgSha should have comment (or a comment on this block) or be unexported
util/showblock/showblock.go:163:1: exported function DumpBlock should have comment or be unexported
util/showblock/showblock.go:211:5: exported var ErrBadShaPrefix should have comment or be unexported
util/showblock/showblock.go:212:5: exported var ErrBadShaLen should have comment or be unexported
util/showblock/showblock.go:213:5: exported var ErrBadShaChar should have comment or be unexported
```
They're *mostly* functionally equivalent, but as the linked play shows, one is considered nil and one is not.  That's because the make version creates a slice header, so it's no longer nil.

I fully agree in most cases it doesn't matter, but if the code is making decisions based on a slice being `== nil`, it could change the behavior.

I just verified that is not the case here since it's using `append`, so there is no problem with this change.  However, I did want to point out that changing these can *potentially* be dangerous so it's important to review how they're used before blindly trusting golint.