Minor changes for Cygwin support

[Jason B. Alonso]

Hello,

There are a couple small changes that were required of me to build guile
under Cygwin.

1) ice-9/and-let*.scm had to be renamed to and-let-star.scm (Which required
changing every reference to and-let*.scm to and-let-star.scm, which is
relatively minor)  I'd give you a diff of this, but my diff efforts failed.

2) libguile/net_db.c had the following chunk of code:

/* Some systems do not declare this. Some systems do declare it, as a
macro. */
#ifndef h_errno
extern int h_errno;
#endif

But Cygwin doesn't define h_errno as a preprocessor symbol, so...

/* Some systems do not declare this. Some systems do declare it, as a
macro. */
#ifndef __CYGWIN__
#ifndef h_errno
extern int h_errno;
#endif
#endif

This is a "hack" so to speak, as this should be done as a configure step
that detects whether or not h_errno is a preprocessor definition, etc.  As I
am not quite an autoconf guru, this had to suffice for me.

With these changes, guile should build (./configure; make; make install)
with no further ado.

Sincerely,

Jason Alonso

p.s. Your bug-reporting page that mentions running diff needs additional
detail (or, alternatively, I need my head examined, as I'm not a diff guru
either):

$ diff -c -r guile-1.4 guile-1.4-orig
Only in guile-1.4-orig/ice-9: and-let*.scm
Only in guile-1.4/ice-9: and-let-star.scm

This does not seem very useful to me.  Calling diff -c -r -N will create a
dump of and-let-star.scm, but it still doesn't find the changes I made to
switch all references to and-let*.scm to and-let-star.scm.