[omniORB] Fixes for C4267 warnings when building for Win 64

[Mike Richmond]

When building omniORB 4.1.4 with MSVC 8 for Win 64 we get warnings  
from the omniORB headers:

stringtypes.h(149) : warning C4267: 'argument' : conversion from  
'size_t' to 'int', possible loss of data
callDescriptor.h(333) : warning C4267: 'argument' : conversion from  
'size_t' to 'int', possible loss of data

These warnings go away if we change _CORBA_String_helper::alloc() to  
take a size_t instead of an int, and change omniCallDescriptor()'s  
op_len_ argument to be a size_t instead of an int.  The latter change  
also fixes similar warnings in the C++ generated from our IDL.

Can these changes be incorporated?  Thanks.

Mike Richmond
Global Graphics Software Ltd