round-trip trees through index_read_index
round-trip trees through index_read_index

Read a tree into an index using `git_index_read_index` (by reading
a tree into a new index, then reading that index into the current
index), then write the index back out, ensuring that our new index
is treesame to the tree that we read.

Corillian/libgit2,stewid/libgit2,stewid/libgit2,Corillian/libgit2,Corillian/libgit2,Corillian/libgit2,stewid/libgit2,Corillian/libgit2,stewid/libgit2,stewid/libgit2,Corillian/libgit2,stewid/libgit2