Slightly improve logging formatting. (#484)
Slightly improve logging formatting. (#484)

This changes the logged votebits when logging that wallet ticket
purchasing is enabled to always display with leading 0s.  For example,
currently for a votebits value of 1, it will be logged as 0x1.  This
changes it to be logged as 0x0001.
jrick/btcwallet,decred/dcrwallet,decred/dcrwallet,jrick/dcrwallet,jrick/btcwallet,jrick/dcrwallet