JNR-46 Callable attribute is not correctly captured for bonds.

We were looking at the MTY_TYPE field, which is actually called MTY_TYP.  This has been changed to use CALLABLE as it's more appropriate.
Reviewed-By:Andrew Griffin
PLAT-5985 Support for SwapIndex

Changed the loader to look at SECURITY_DES for the string ISDAFIX rather than
INDX_SOURCE, which proved unreliable for non-US currencies.
Reviewed-By:Chris Kent