[git] Improve `mpr` command
[git] Improve `mpr` command

Change the `mpr` command so that it merges the specified pull request
into the current branch¹, or if a branch name is specified², into the
specified branch.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

¹ git mpr <number>
² git mpr <number> <branch_name>

EDiLD/dotfiles,oddlord/dotfiles,mickael83/ubuntu-dotfiles,zlot/dotfiles,wingy3181/dotfiles,wingy3181/dotfiles,girishramnani/dotfiles,pbrooks/dotfiles,zlot/dotfiles,AlbertoElias/dotfiles,makabde/dotfiles,christophermoura/dotfiles,mickael83/ubuntu-dotfiles,newtonne/dotfiles,christophermoura/dotfiles,AlbertoElias/dotfiles,newtonne/dotfiles,wingy3181/dotfiles,makabde/dotfiles,EDiLD/dotfiles,girishramnani/dotfiles,b-boogaard/dotfiles