This changes the behavior of object parsing for commits and tags
so that even when bad data is found inside the object, we will
continue to try to parse as much of the object as we can.  The
existing functions (`git_object_lookup` for example) will still
delete the partially parsed object before returning an error, but
this also adds a new function `git_object_lookup_lax` that will
still return the error, but will also return the object with the
partial data (if we got far enough along in the parsing process to
even create the base object).

Better global search path sandboxing in tests

There are a number of tests that modify the global or system
search paths during the tests.  This adds a helper function to
make it easier to restore those paths and makes sure that they
are getting restored in a manner that preserves test isolation.

Initialize local variable

Increase config snapshot usage

Add R bindings to the README

And decrease extra reload checks of config data.