This fixes a filebase corruption issue that could be triggered by using
FileBase.update() to rename a file while also changing the file's auxdata or
extended description: you can't remove a file header that has the new filename
(in the file_t.name field), cause it doesn't exist yet. So we needed an SMBLIB
API function to pass the (original) filename instead. Much like the filedat.c
removefile() function, but without the SMB opening/closing feature.