Fix up getlocalbase() implementation

[scottl]

Summary

There are several problems with data types, casts, and checks in
getlocalbase(). This attempts to fix them

[jrtc27]

lib/libutil/getlocalbase.c

77

strlcpy doesn't include the NUL so this to stay >=.

[jrtc27]

lib/libutil/getlocalbase.c

53–54

This should probably be EINVAL (and could then be folded into the previous if).

[scottl]

Fix items suggested by Jessica, move to sysctlnametomib() to account for
inconsistencies in the user/kernel interface

[scottl]

Remove extra debugging

[jrtc27]

lib/libutil/getlocalbase.c

60

miblen is currently uninitialised before the call; presumably it works because it's reading random garbage on the stack that's most likely >= 2. You should probably also be checking the return value here.