Using platform independent variables when writing/loading values from StreamIndexedIO.

The changes in the file format introduced in Cortex 8 came with 32 bit values that were saved from "unsigned int" variables. But that is platform dependent.
They have been replaced now by int32_t to garantee that the files can be loaded on 32bit platform.

Added some extra checks to prevent these values to overflow, preventing corrupted files.
Addressing comments by John.
Merge pull request #227 from ldmoser/streamIndexedIOmultiPlatform

Using platform independent variables when writing/loading values from StreamIndexedIO