BlockBed.cpp: Fixed Multiple people in one bed.

OnUse in BlockBed.cpp now checks whether bit flag 0x4 in the Data values of the bed is set before somebody can try to sleep in the bed.
BlockBed.cpp: Fixed space at if statement

Added a space after an if statement and before the first bracket to keep up code conventions.
Merge pull request #702 from TheJumper/master

BlockBed.cpp: Fixed Multiple people in one bed.