Previously opendir("/data") would fail if filesystem with "data" prefix
was registered in VFS, while opendir("/data/") would succeed.
This change fixes handling for the former case and adds relevant tests.
- fix null pointer dereference in VFS when VFS implementations are added
and removed in different order
- vfs_fat_sdmmc, vfs_fat_spiflash: pass correct drive to mkfs
(previously it would always do mkfs in the first drive)
- add test case
- spaces->tabs in tasks.c
- update vfs_uart.c to use per-UART locks
- add license to vfs_uart.c
- allocate separate streams for stdout, stdin, stderr, so that they can be independently reassigned
- fix build system test failure
- use posix off_t instead of newlib internal _off_t
