f20-build tags were created with wrong arches (i386, x86_64) on secondary kojis, I've fixed ppc and s390

eg.
{{{
dan@eagle ~]$ arm-koji taginfo f20-build
Tag: f20-build [131]
Arches: i686 x86_64
This tag is a buildroot for one or more targets
Current repo: repo#249229: 2013-03-14 12:19:58.292282
Targets that build from this tag:
f20-candidate
f20
rawhide
Inheritance:
0 .... f20-override [130]

1 .... f19-build [117]

}}}