Handle tags that do not have a tagger.

Not all tags have a tagger. For example, the v2.6.11 tag on the linux repository does not have a tagger. For these cases, return null for the Tagger property on a tag annotation.
Update logic in Proxy to re-use taggerHandle
FastForward merge should block if there are checkout conflicts.

Currently, if there are changes in your working directory and
a fastforward merge would update those files, the checkout
that is performed as part of the fast forward will skip over
these files. This change fixes and adds regression tests around
this behavior.
Update binaries to 091165c

https://github.com/libgit2/libgit2/compare/e93206e...091165c
Fix for osx CI script
Index.Stage: do not stage ignored files

Stage() now respects ignore files by default, similar to git.git.
Users accustomed to the old behavior may use the new StageOptions
class (in particular the IncludeIgnored bool) to override this
behavior.
Update binaries to 69db893

https://github.com/libgit2/libgit2/compare/091165c...69db893
Enforce Clone() test coverage

Fix #701
Ensure Tags can be created in detached Head state

Fix #791
Minor fix
Remove trailing whitespaces
Drop tests that rely on the global configuration

We cannot make correct assumptions regarding the fact that the
environment that host the test runner:

 - Contains a global git config file
 - Grants the test runner process with enough rights to write to this file
 - That this file already contains an expected entry

Given those constraints, those tests are removed.
Release LibGit2Sharp v0.19
Use new Resharper shared solution based settings