Simplify check for trusted certificates.

This changes the previous check for untrusted certs to a check for
certs explicitely marked as trusted.
The change is backward-compatible (tested with certdata.txt v1.80).
md5: remove use of CommonCrypto-to-OpenSSL macros for the benefit of Leopard

For some reason, OS X 10.5's GCC suddenly stopped working correctly with
macros that change MD5_Init etc. in the code to CC_MD5_Init etc., so I
worked around this by removing use of the macros and inserting static
functions that just call CommonCrypto's implementations of the functions
instead.
FTP: when EPSV gets a 229 but fails to connect, retry with PASV

This is a regression as this logic used to work. It isn't clear when it
broke, but I'm assuming in 7.28.0 when we went all-multi internally.

This likely never worked with the multi interface. As the failed
connection is detected once the multi state has reached DO_MORE, the
Curl_do_more() function was now expanded somewhat so that the
ftp_do_more() function can request to go "back" to the previous state
when it makes another attempt - using PASV.

Added test case 1233 to verify this fix. It has the little issue that it
assumes no service is listening/accepting connections on port 1...

Reported-by: byte_bucket in the #curl IRC channel