Convert cvs_masters and rev_masters to arrays

Read the original file list into an array and sort in path_deep_compare
order. This order is preserved in the array of cvs masters and the
array of rev masters.

Cuts about 10% off the merge phase.
Change cvs_repo from linked list to array

Remove the next pointer from cvs_master and teach everything
that it is an array.

Simplify comparison in export_commit.

The masters array is sorted in path_deep_compare order
so we can compare on address rather than calling the comparator
Documentation and comment fixes.