Merge #8880: protocol.h: Move MESSAGE_START_SIZE into CMessageHeader

1df3111 protocol.h: Make enums in GetDataMsg concrete values (Wladimir J. van der Laan)
2c09a52 protocol.h: Move MESSAGE_START_SIZE into CMessageHeader (Wladimir J. van der Laan)
f9bd92d version.h: s/shord/short/ in comment (Wladimir J. van der Laan)