BRAM unlock bit should be able to re-lock

[dshadoff]

Backup memory unlock bit (0x1807 bit 7) is set to unlock BRAM (i.e. set 0x1807 = 0x80).
Normally, BRAM is re-locked by reading 0x1803, but can also be locked by resetting bit of 0x1807 (i.e. same as above but the bit is reset).

[dshadoff]

Hmm... there appear to be no restrictions/locking on BRAM for HuCard games; only CDROM...

[dshadoff]

Notes:
The physical (and logical) memory will (or should) only show BRAM data if the BRAM is unlocked.
The "BRAM" page of memory editor shows the data regardless of lock.

The HuCard BRAM apparently doesn't implement locking.
The CDROM BRAM - while it implements locking and unlocking - was improperly locking the BRAM when the debugger screen was displayed, due to inappropriate behaviour when a "silent" read takes place for the purposes of refreshing the display.
This improper CDROM behaviour is being dealt with in issue #112 .

Neither of these systems was dealing with the "re-lock" data value on the lock bit.

[dshadoff]

Re-locking behaviour has had a Pull Request submitted.

The HuCard improper locking now has a new issue created against it (HuCard BRAM defaults to visible) - issue #136