Add option to disable 077 umask (create new files with system default umask)

The option is only effective for either wallet-less builds or if
-disablewallet is specified as well.
Correcting to account for jgarzik's feedback
Make -sysperms without -disabledwallet a fatal error wallet-enabled builds
Simplify code, as per laanwj's suggestion
leave the command-line options sorted within their category
Merge pull request #4286

7e09b36 leave the command-line options sorted within their category (Rune K. Svendsen)
d53a33b Simplify code, as per laanwj's suggestion (Rune K. Svendsen)
bd4307b Make -sysperms without -disabledwallet a fatal error wallet-enabled builds (Rune K. Svendsen)
4e1a196 Correcting to account for jgarzik's feedback (Rune K. Svendsen)
34d5fc0 Add option to disable 077 umask (create new files with system default umask) (Rune K. Svendsen)