evolve: set the second parent if we get conflicts while evolving
This patch makes sure we set the second parent correctly if we run into
conflicts while evolving. Also, we need to make sure to reset to one parent
before committing.
evolvecmd: import mercurial.node module as nodemod
We use node as a variable name at few places and the conflicts with variable
name are not good. Moreover this practice is followed in core mercurial also.