darwinssl: PKCS#12 import feature now requires Lion or later

It turns out that some of the constants necessary to make this feature
work are missing from Snow Leopard's Security framework even though
they are defined in the headers.

Bug: http://curl.haxx.se/mail/lib-2013-11/0076.html
Reported by: myriachan

docs/libcurl/curl_easy_setopt.3

@@ -2375,7 +2375,7 @@ prefix, in order to avoid confusion with a nickname.
 Pass a pointer to a zero terminated string as parameter. The string should be
 the format of your certificate. Supported formats are "PEM" and "DER", except
 with Secure Transport. OpenSSL (versions 0.9.3 and later) and Secure Transport
-(on iOS 5 or later, or OS X 10.6 or later) also support "P12" for
+(on iOS 5 or later, or OS X 10.7 or later) also support "P12" for
 PKCS#12-encoded files. (Added in 7.9.3)
 .IP CURLOPT_SSLKEY
 Pass a pointer to a zero terminated string as parameter. The string should be

lib/curl_darwinssl.c

@@ -938,8 +938,10 @@ static OSStatus CopyIdentityFromPKCS12File(const char *cPath,
     cPassword, kCFStringEncodingUTF8) : NULL;
   CFDataRef pkcs_data = NULL;
 
-  /* We can import P12 files on iOS or OS X 10.6 or later: */
-#if CURL_BUILD_MAC_10_6 || CURL_BUILD_IOS
+  /* We can import P12 files on iOS or OS X 10.7 or later: */
+  /* These constants are documented as having first appeared in 10.6 but they
+     raise linker errors when used on that cat for some reason. */
+#if CURL_BUILD_MAC_10_7 || CURL_BUILD_IOS
   if(CFURLCreateDataAndPropertiesFromResource(NULL, pkcs_url, &pkcs_data,
     NULL, NULL, &status)) {
     const void *cKeys[] = {kSecImportExportPassphrase};
@@ -963,7 +965,7 @@ static OSStatus CopyIdentityFromPKCS12File(const char *cPath,
     CFRelease(options);
     CFRelease(pkcs_data);
   }
-#endif /* CURL_BUILD_MAC_10_6 || CURL_BUILD_IOS */
+#endif /* CURL_BUILD_MAC_10_7 || CURL_BUILD_IOS */
   if(password)
     CFRelease(password);
   CFRelease(pkcs_url);