scsh port to the Hurd

[Andreas Voegele]

I've modified the Scheme shell scsh, which is available at
http://www.scsh.net/, so that it can be built on Hurd systems.
My patch for scsh 0.6.4 is available at
http://home.pages.de/~voegele/scsh-gnu.html.

I'm interested in bug reports and in your opinion on the following
name mappings.

Scsh maps several definitions from /usr/include/bits/fcntl.h to Scheme
symbols.  For example, on all supported systems the following symbols
(among others) are defined:

O_RDONLY -> open/read
O_WRONLY -> open/write
O_RDWR   -> open/read+write
O_NOCTTY -> open/no-control-tty

I decided to map the Hurd-specific definitions to the following
symbols:

O_EXEC        -> open/execute
O_NOLINK      -> open/no-link
O_NOTRANS     -> open/no-translator
O_NOATIME     -> open/no-access-time
O_IGNORE_CTTY -> open/ignore-control-tty

What do you think about these names?  I'm open to alternative
suggestions (but I won't accept abbreviations like open/noatime since
none of the other supported systems uses abbreviated names).