The test wasn't correctly excluding instructions, so it was possible
to create a situation where a two-byte data item had an instruction
starting in the second byte.
We also weren't checking the length of the instruction to ensure that
it was wider than the reloc data. This could get weird for an
immediate constant when the M/X flags are wrong. When in doubt, don't
overwrite.
The decision of how to handle indeterminate M/X flag values is made in
StatusFlags. This provides consistent behavior throughout the app.
This was being done for M/X but not for E.
This change also renames the M/X tests, prefixing them with "Is" to
emphasize that they are boolean rather than tri-state.
There should be no change in behavior from this.
