Updated links

 * Codewright is end-of-lifed by Borland.
   According to the wikipedia page it has been aquired by Embarcadero
   Software, but if I search their web page there are 0 hits on
   the name CodeWright and also no relevant hits when searching for
   'perl'.

 * tcsh hardly seems relevant anymore and the link to the 'book' is
   broken. I can't find any similar 'book' on the web.

 * MKS and U/WIN are not available anymore for Win32.

 * Updated cygwin web link.

 * Remark on transferring files via FTP seems out of place here.

 * MacPerl is not a product anymore so its editor no longer a viable
   IDE.

 * Affrus is no longer to be found on the product website.

 * The Alpha editor had its last release more than 12 years ago.
Merge pull request #54 from mbeijen/perlfaq3-upd

perlfaq3: updated some links.