* Add a MIPS-I (r3000) exception handler to the Pica locore.S.
Change the names of the masks used to extract the exception code
to the new MIPS_xxx names.
* Rename the vector code from MachException() to
mips_r4000_exception, in both locore and in the init_main()
code that copies it from locore to the exception vector locations.
* Change the locore and C code to use the new MIPS_SR_INT_IE
name for the Status register master interrupt-enable bit.
Similar changes to the pmax equivalents are in progress.
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