socket.error is deprecated even in upstream:
https://docs.python.org/3/library/socket.html#socket.error,
and never was a part of MicroPython socket API.

This was apparently of an ::only directive which was later removed.

It's very low, hardware level, with associated constraints on operations
and callbacks.

To enable options which may be incompatible with other boards, etc.

Overriding CONF_FILE in "minimal" target itself is too late due to include-
pinned $(Z_EXPORTS) target.

From https://github.com/micropython/oofatfs, branch work-R0.12b,
commit 1e295b40550664bbaac18d95a4b6a58154464d31.

They disappeared when stmhal changed to use new MICROPY_VFS code.

This patch makes the following configuration changes:
- MICROPY_FSUSERMOUNT is disabled, removing old mounting infrastructure
- MICROPY_VFS is enabled, giving new VFS sub-system
- MICROPY_VFS_FAT is enabled, giving uos.VfsFat type
- MICROPY_FATFS_OO is enabled, to use new ooFatFs lib, R0.12b

User facing API should be almost unchanged.  Most notable changes are
removal of os.mkfs (use os.VfsFat.mkfs instead) and pyb.mount doesn't
allow unmounting by passing None as the device.

It should only be used for low-level things and with caution, for example
putting mounted VFS data in ROM or the static data section.

The vfs_fat_fsusermount test is no longer relevant so has been removed.

The VFS sub-system supports mounting of an arbitrary number of devices
(limited only by available RAM).  The internal flash is now mounted at
"/flash".

This patch includes a new module "uos_vfs" which can be used for testing
the VFS syb-system.

The VfsFat object can now be mounted by the generic VFS sub-system.

This provides mp_vfs_XXX functions (eg mount, open, listdir) which are
agnostic to the underlying filesystem type, and just require an object with
the relevant filesystem-like methods (eg .mount, .open, .listidr) which can
then be mounted.

These mp_vfs_XXX functions would typically be used by a port to implement
the "uos" module, and mp_vfs_open would be the builtin open function.

This feature is controlled by MICROPY_VFS, disabled by default.

And move declaration of mp_fat_vfs_type to this file.

The new version of FatFs requires a minimum of 50 blocks on the device.
Also, some tests no longer make sense with an OO vfs.

If MICROPY_VFS_FAT is enabled by a port then the port must switch to using
MICROPY_FATFS_OO.  Otherwise a port can continue to use the FatFs code
without any changes.

From https://github.com/micropython/oofatfs, branch work-R0.12b,
commit a346ccec123c2e4d887e2751d64156208d03bff4.

Previous to this patch the qemu-arm tests were compiled with is_relp=true
meaning that the __repl_print__ function was called for all lines of code
in the outer scope.  This is not the right behaviour for scripts that are
executed as though they were a file (eg tests).

With this fix the micropython/heapalloc_str.py test now works so it is
removed from the test blacklist.

Starts with concatenation with an empty string.