Once I added tests for the whitespace handling options of
diff, I realized that there were some bugs. This fixes
those and adds the new tests into the test suite.
This gets the basic plumbing in place for git_diff_blob.
There is a known issue where additional parameters like
the number of lines of context to display on the diff
are not working correctly (which leads one of the new
unit tests to fail).
This adds APIs for querying git attributes. In addition to
the new API in include/git2/attr.h, most of the action is in
src/attr_file.[hc] which contains utilities for dealing with
a single attributes file, and src/attr.[hc] which contains
the implementation of the APIs that merge all applicable
attributes files.
