MegaST v0.4.14 beta: restored hard disks work, mouSTer right button fix

Pre-release for testing. Please report what works and what doesn't in the issues (core version, board, TOS, machine settings, disk image).

Fixed

• Hard disk not seen by TOS after power-on (#11, #12): since 0.4.12 the core restores the remembered images at power-on and after a long press of the reset button, but it ejected them again right away inside the core, while the menu still listed them. Images mounted in the menu while the ST was running were not affected. "Reset Atari ST" in the menu ejected the images, too. Please test: mount your hard disk image, switch off and on, and check that TOS shows its drives.
• Right mouse button stuck with a mouSTer (#17): pin 9 of the mouse port has no pull-up on the MEGA65, so a mouSTer that leaves it open (or a joystick in the mouse port) looked like a held right button, and GEM ignored clicks on window controls. The core now ignores the right button until it has seen pin 9 released. An Atari or Amiga mouse keeps its right button; a mouSTer in Atari mode has none.

Files

Unchanged menu: the 99 byte atarist/stcfg and the 1536 byte atarist/stmount of 0.4.12 and 0.4.13 stay valid (stmount lets the core remember the mounted images, #13). Coming from 0.4.7 or older, copy the new atarist/stcfg from the zip, otherwise the settings are not saved. Hard disk images written with 0.4.10 or older may be damaged (#11): restore them from a backup.

File	Board	Status
MegaST-R6-v0.4.14.cor	MEGA65 R6	developer's board
MegaST-R5-v0.4.14.cor	MEGA65 R5	not tested yet, please report
MegaST-R4-v0.4.14.cor	MEGA65 R4	not tested yet, please report
MegaST-R3-v0.4.14.cor	MEGA65 R3/R3A (no SDRAM)	working on an R3A (#2); 512 KB ST RAM, no Viking, no STEroids

All changes: VERSIONS.md, manual: README.

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