certsync: Please test patches on systems < 10.9

[Clemens Lang]

Hi,

> Some warnings on Tiger, but it builds and seems to work.
> 
> certsync.m: In function 'certificatesForTrustDomain':
> certsync.m:298: warning: implicit declaration of function
> 'SecTrustSettingsCopyTrustSettings'
> certsync.m: In function 'exportCertificates':
> certsync.m:406: warning: implicit declaration of function
> 'SecCopyErrorMessageString'
> certsync.m:406: warning: passing argument 1 of 'PLCFAutorelease' makes
> pointer from integer without a cast
> certsync.m:426: warning: passing argument 1 of 'PLCFAutorelease' makes
> pointer from integer without a cast

Only worked because it didn't actually use these functions:
 - SecTrustSettingsCopyTrustSettings wasn't used because it is only used
   in a block that's specific to >= 10.5 anyway – adding the declaration
   to compat.h should have fixed that.
 - SecCopyErrorMessageString would have crashed if an error actually
   occured. I changed the code to avoid the function if it isn't defined.

Changes in r124891.

-- 
Clemens Lang