Resolve BOOL vs. char type bug

Updates the type checking in OCMBoxedReturnValueProvider's
handleInvocation method so it's closer to the system used
by the main OCMock project on TOT.  The new implementation
uses a helper method, -[NSValue getBytes:objCType:], which
treates 'B' and 'c' types as equivalent.

Note: NSValue+OCMAdditions and the meat of the new implementation
of handleInvocation are both copied from the main OCMock project
(at revision 999b843).  Anyone looking for a useful history of
this code will need to search in the main OCMock project.