Misc fixes

Hey Cornelius,

cpansearch has been broken and uncompilable on my machine for awhile.  This branch contains several fixes to help get cpansearch working again.

 * The first patch fixes a GCC warning about a missing sentinal.
 * The second patch sets www.cpan.org to be the default mirror, since cpan.perl.org provides a 301 Redirect rather than packages.gz.  If cpans tries to unzip the html, it segfaults.
 * The third patch gets the build working on OS X by move the -l flags to LDFLAGS and using the system curl
 * The fourth patch is just some miscellaneous cleanups to Makefile

Please let me know if you'd like me to make any changes.  Take care and thank you for writing this program.  I've found it very handy.  Have a great new year!

Cheers,
Fitz Elliott