`cmd_fbrowse` fails with folders with spaces in the name

Title says it all. Attempting to browse to a folder e.g. 'my folder' from within 'cmd_fbrowse' will cause 'cd' to fail with `sh: line 1: cd: too many arguments`.

I think you probably just need to quote it =D

## Steps to Reproduce:
```
$ mkdir 'my folder'
$ mle
cmd_fbrowse (C-b)
>select 'my folder'
`sh: line 1: cd: too many arguments`
```