IndexFile.add: Fixed incorrect path handling if path rewriting was desired and absolute paths were given

Commit.create_from_tree: fixed critical bug that would cause it to create a branch named master by default, instead of the reference actually set ( which is master in many, but not all cases )
 - in fact it could be detached as well, we would fail ungracefully although we could assume master then ... although we cant really make the decision
Repo.is_dirty: improved its abiility to deal with empty repositories and a missing head. Weird thing is that the test always worked fine with the previous code, but it didn't work for me in a similar situation without this change at least

Author: Byron

Diff for: lib/git/index.py

@@ -907,8 +907,9 @@ def add(self, items, force=True, fprogress=lambda *args: None, path_rewriter=Non
                 must be a path relative to our repository.
 
                 If their sha is null ( 40*0 ), their path must exist in the file system
-                as an object will be created from the data at the path.The handling
-                now very much equals the way string paths are processed, except that
+                relative to the git repository as an object will be created from 
+                the data at the path.
+                The handling now very much equals the way string paths are processed, except that
                 the mode you have set will be kept. This allows you to create symlinks
                 by settings the mode respectively and writing the target of the symlink
                 directly into the file. This equals a default Linux-Symlink which
@@ -945,6 +946,7 @@ def add(self, items, force=True, fprogress=lambda *args: None, path_rewriter=Non
             is not identical to the layout of the actual files on your hard-dist.
             If not None and ``items`` contain plain paths, these paths will be
             converted to Entries beforehand and passed to the path_rewriter.
+            Please note that entry.path is relative to the git repository.
 
         :return:
             List(BaseIndexEntries) representing the entries just actually added.
@@ -962,8 +964,9 @@ def add(self, items, force=True, fprogress=lambda *args: None, path_rewriter=Non
 
         if paths and path_rewriter:
             for path in paths:
-                abspath = os.path.join(self.repo.working_tree_dir, path)
-                blob = Blob(self.repo, Blob.NULL_HEX_SHA, os.stat(abspath).st_mode, path)
+                abspath = os.path.abspath(path)
+                gitrelative_path = abspath[len(self.repo.working_tree_dir)+1:]
+                blob = Blob(self.repo, Blob.NULL_HEX_SHA, os.stat(abspath).st_mode, gitrelative_path)
                 entries.append(BaseIndexEntry.from_blob(blob))
             # END for each path
             del(paths[:])
@@ -1197,8 +1200,6 @@ def move(self, items, skip_errors=False, **kwargs):
 
         return out
 
-
-
     @default_index
     def commit(self, message, parent_commits=None, head=True):
         """

Diff for: lib/git/objects/commit.py

@@ -357,9 +357,9 @@ def create_from_tree(cls, repo, tree, message, parent_commits=None, head=False):
                 try:
                     repo.head.commit = new_commit
                 except ValueError:
-                    # head is not yet set to master - create it and set it
+                    # head is not yet set to the ref our HEAD points to.
                     import git.refs
-                    master = git.refs.Head.create(repo, 'master', commit=new_commit)
+                    master = git.refs.Head.create(repo, repo.head.ref, commit=new_commit)
                     repo.head.reference = master
                 # END handle empty repositories
             # END advance head handling 

Diff for: lib/git/repo.py

@@ -526,7 +526,7 @@ def is_dirty(self, index=True, working_tree=True, untracked_files=False):
         default_args = ('--abbrev=40', '--full-index', '--raw')
         if index: 
             # diff index against HEAD
-            if os.path.isfile(self.index.path) and \
+            if os.path.isfile(self.index.path) and self.head.is_valid() and \
                 len(self.git.diff('HEAD', '--cached', *default_args)):
                 return True
         # END index handling