pull: move `remote` argument into pull object One more step toward a more modular pull function.

pull: introduce a pulloperation object This object will hold all data and state gathered through the pull. 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 pull 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 function.

tests: lines with largefile .* file://$TESTTMP also match on windows on windows, largefile paths are written as "file:///C:/temp/...", corresponding to "file:///$TESTTMP/..." (all three slashes shown). But on posix systems they are written as "file:///tmp/..." corresponding to "file://$TESTTMP/..." (only two slashes shown). Write the glob "file:/*/" to match both versions.