hg: note that islocal only accepts paths pointing to repos hg.islocal doesn't work for paths pointing to non-repos, such as patch files.

hg.openpath: use url.islocal to tell if the path is local (issue3624) Previously we used hg.islocal, which doesn't work for paths pointing to non-repos, such as patch files.

util.url: add an 'islocal' method This returns True if the URL represents a path that can be opened locally, without needing to go through the entire URL open mechanism.

push: move bookmarks exchange in the exchange module The bookmark exchange code was already extracted during a previous cycle. This changesets moves the extracted function in this module. This function will read and write data in the `pushoperation` object and It is preferable to have all core function collaborating through this object in the same place. This changeset is pure code movement only. Code change for direct consumption of the `pushoperation` object will come later.

push: move `newbranch` argument into the push object One more step toward a more modular push function.

push: move `revs` argument into the push object One more step toward a more modular push function.

push: move `force` argument into the push object One more step toward a more modular push function.

push: move `remote` argument in the push object One more step toward a more modular push function.

push: ease access to current ui object The `pushoperation.repo.ui` attribute is very commonly used. we offer a faster way to access it directly through the push operation object.

push: introduce a pushoperation object This object will hold all data and state gathered through the push. This will allow us to split the long function into multiple small one. Smaller function will be easier to maintains and wrap. The idea is to blindly store all information related to the push in this object so that each step and extension can use them if necessary. We start by putting the `repo` variable in the object. More migration in other changeset.