If --enable-pythoninterp is specified on the command line and Python is not 
found in the path, then Vim will build anyway without the Python interpreter. 
This patch to configure.in makes sure that ./configure fails without continuing.

I plan to implement more checks like that in the branch 
'autoconf-error-on-unattainable-features' here:

http://code.google.com/r/shlomif-changes/

Regards,

-- Shlomi Fish