test: fix compilation warning
errno: add ETXTBSY

Add `ETXTBSY` which could be returned by file system reads on some
unixes and emulate it with -148 (`ERROR_PATH_BUSY`) on windows.
test: fix compiler warning
test: fix compilation warning on non-linux systems
fsevent: rename filename field to path

Also, it's now considered private.
unix, windows: add uv_fs_event_getpath