Repeated forward slashes become absolute paths

[g5t]

Following up on #204 and the fix in #205, I noticed that a path with repeated forward slashes will silently ignore any valid path before the last such '/' and treat the rest of the path specification as an absolute path. E.g., a NeXus HDF5 file with an NXinstrument group at /entry/instrument opened as file will pass the following assert statement

assert id(file['/entry/instrument']) == id(file['/entry//entry/instrument'])

this behavior is contrary to file system paths under unix-like systems which treat repeated path separators as if they were singular.

[MridulS]

Maybe we can use pathlib to santize these things? I know they aren't path objects, but it should take care of all these corner cases.

[jl-wynen]

Yes:

PurePosixPath('/entry//entry/instrument').as_posix()

Also takes care of the final slash