Description of the problem (starting with 61be7a1):

When starting a new experiment, creating a fresh ODB and than adding the 
directory '/Custom', the mhttpd runs into a problem on RHEL/Fedora, but not on 
Ubuntu and macOS. When trying to open the ODB from within whatever browser I get 
the following error message in the midas message queque:

[mhttpd,ERROR] [mhttpd.cxx:563:rread,ERROR] Cannot read file '/root', read of 
4096 returned -1, errno 21 (Is a directory)

and in the browser I get a popup which tries to save a file called 'root'.

I track this down to the following: in mhttpd, interprete (line 18046) it is 
check if a custom page file exists (ss_file_exist) and if yes, it tries to 'load' 
it. Now, at this stage the variable dec_path contains '/root'.

Here now what goes wrong: ss_file_exist tries to open the given path, and if a 
valid file descriptor is returned it assumes the file exists. This is not 
perfectly correct since it also will get a valid file descriptor is path is an 
accessible directory!

Now for whatever reason, on RHEL/Fedora '/root' will return a valid file 
descriptor, but not on macOS and Ubuntu. Others I haven't tested. A possible fix 
would be to check explicitly if path is a directory and if yes return 0 in 
ss_file_exist (see attached diff).

Perhaps there is cleaner way to deal with this issue?!