Description of problem:

From the manpage (substituted foo with example):

|        For example, to be able to use GPG to sign packages as the user "John | Doe <jdoe>" from the key rings located in /etc/rpm/.gpg using 
| the  executable
|       /usr/bin/gpg you would include
|
|       %_signature gpg
|       %_gpg_path /etc/rpm/.gpg
|       %_gpg_name John Doe <jdoe>
|       %_gpgbin /usr/bin/gpg

But changing %_gpgbin has no effect.

Version-Release number of selected component (if applicable):
rpm-4.6.0-0.rc1.8

How reproducible:
always

Steps to Reproduce:
1. change %_gpgbin in ~/.rpmmacros to /bin/false
  
Actual results:
gpg can still sign rpms

Expected results:
it should fail

Additional info:
In case you wonder, why I would like to change the executable: I wanted to pass  --force-v3-sigs --digest-algo=sha1 to gpg when using --addsign and the only possble way to do this seems to use a wrapper for gpg and specifying this to rpm, but of course using the __gpg macro. But I guess this macro is not intended for this and may break other stuff.