bup index: fix progress message printing when using -v.
bup index: fix progress message printing when using -v.

It wasn't printing often enough, and thus was absent more often than
present.

ToxicFrog/bup,gevaerts/bup,tjanez/bup,apenwarr/bup,jbaber/bup,pombredanne/bup,gevaerts/bup,mhoeher/bup,tjanez/bup,mhoeher/bup,pombredanne/bup,mhoeher/bup,jbaber/bup,ToxicFrog/bup,ToxicFrog/bup,tjanez/bup,tjanez/bup,apenwarr/bup,pombredanne/bup,tjanez/bup,mhoeher/bup,ToxicFrog/bup,gevaerts/bup,gevaerts/bup,jbaber/bup,pombredanne/bup,pombredanne/bup,tjanez/bup,gevaerts/bup,mhoeher/bup,pombredanne/bup,jbaber/bup,mhoeher/bup,ToxicFrog/bup,apenwarr/bup,apenwarr/bup,jbaber/bup,jbaber/bup