filecache: make 'join' abstract All subclasses redefine this method, so we can make it abstract.

filecache: explicitly test 'repofilecache' The tests is actually about testing a repofilecache (it uses a fake repo). We make this clear to prevent blockers while cleaning theses API.

repofilecache: directly use 'repo.vfs.join' The 'vfs' attribute already have all methods we need, the value of going through the repository for this is low. so we removes it.

repofilecache: define a 'join' method We are about to turn the 'join' method of the base class Abstract, so we need on to be defined in the localrepo. The ultimate goal here is to be able to stop relying for the 'localrepo' class to have a 'join' methods (there is above one hundred methods on 'localrepo'. This change make te 'repo' file cache have its own code so that we can prepare this change to the repostory class. explicite join

wix: add censor docs to installer script Spotted by Matt Harbison.

internals: add some brief documentation about censor

localrepo: rename proxycls to filteredrepo When debugging in a Python shell, the type of "repo" is "proxycls", which could confuse new people. In [1]: repo Out[1]: <mercurial.localrepo.proxycls at 0x7f65d4b976d0> Let's rename it to "filteredrepo" to make it clearer.