hgweb: don't responsd to api requests unless feature is enabled Per discussion at https://phab.mercurial-scm.org/D2834, new URLs in hgweb can conflict with subrepos and virtual repos. This may prevent access to repos in certain paths or having certain names. Until we have a workaround for this, let's not serve requests for "api/" URLs unless the feature is enabled. Differential Revision: https://phab.mercurial-scm.org/D2936