a program to print out the error strings for winsock errors
use FormatMessage for winsock errors

as discussed here:
http://archives.seul.org/libevent/users/Feb-2013/msg00004.html
make sure caching works, and we don't leak memory
use hashtable instead of linked list to cache winsock errors

as discussed here:
https://github.com/libevent/libevent/pull/41#issuecomment-13611817
test filling up the hash table a bit
Merge pull request #41 from ppelleti/winsock-errs

FormatMessage for winsock errors