https+auth: use a ~/.git-credentials file if it exists to fetch credentials

In some situations we code the plain auth-less uri in the hgrc paths
section (for convenience) and want to use a centrally-stored
credentials file.

Though it is possible to use the hgrc [auth] section, it would be also
nice to access .git-credentials (still usefull for git direct access),
avoiding double maintenance of credentials.

This probably does not cover all possible situations with git
credentials handling (a vast topic) but it provides a working

closes 305
1 files changed, 9 insertions(+), 0 deletions(-)

M hggit/
M hggit/ +9 -0
@@ 1742,6 1742,15 @@ class GitHandler(object):
                     username = username.decode('latin-1')
                 if password is not None:
                     password = password.decode('latin-1')
+            if url.user is None:
+                username_password = client.get_credentials_from_store(
+                    url.scheme,
+                )
+                if username_password is not None:
+                    username, password = username_password
+                    username = username.decode('utf-8')
+                    password = password.decode('utf-8')
             return (