bundle-spec: properly parse boolean configuration as boolean Before this changesets "v2;revbranchcache=no" would actually request the addition for a revbranchcache part as the non-empty string `"0"` is `True`

bundle-spec: properly identify changegroup-less bundle It is possible to produce a bundle without changegroup. For example if we want to only send phases or obsolescence information. However that lead to crash for command that identifies bundle content. So we fix that. The test will come in the next changesets, when we fix another bug preventing to generate such bundle by hand.