import-checker: use any() and a genexp to avoid awkward for/else construction

import-checker: backout 40f79b9a2cc8 (issue4129) This patch backs out 40f79b9a2cc8, which caused test-module-imports.t to be skipped when the test was run using virtualenv. Since the test now passes when using virtualenv, the skip is no longer necessary.

import-checker: make test-module-imports.t work using virtualenv (issue4129) This patch modifies contrib/import-checker.py so that test-module-imports.t will pass if run using virtualenv. The patch achieves this by adding two new prefixes to the list of allowable sys.path prefixes. The added prefixes are the directories of two modules in the stdlib. The modules selected are a minimal set that allowed the return value of list_stdlib_modules() to match the return value without virtualenv, when run on the patch author's machine: Mac OS X 10.8, Python 2.7.6.

import-checker: refactor sys.path prefix check (issue4129) This patch refactors the logic in contrib/import-checker.py responsible for checking the beginnings of the paths in sys.path. In particular, it adds a variable that defines the set of allowed prefixes. The primary purpose of this change is to make it easier to add more allowed prefixes. This will be useful in resolving issue4129, which involves making the function list_stdlib_modules() work when run from a virtualenv.

filter: add a comment so that people do not forget to update subsettable Changeset 175c6fd8cacc moved `subsettable` from `mercurial/repoview.py` to `mercurial/branchmap.py`. This mean that `filtertable` and `subsettable` are no longer next to each other. So we add a comment to remind people to update both.

localrepo: remove unused repo.branchtags()/_branchtip() methods