Patch to src/Makefile.in for GPERF

[John W. Eaton]

On  6-Feb-2009, John Swensen wrote:
| Here is the promised patch for checking for the version number, rather  
| than a test on a snippet of code.  I don't know if this is the right  
| way to do this, but saw several examples on other mailing lists using  
| this sort of check for version number.

We should avoid testing for version numbers if at all possible.
So please fix the feature test instead.

jwe