Fix Mopidy version when run from another Git repo (related to #706)

docs/changelog.rst

@@ -13,6 +13,12 @@ v0.19.1 (UNRELEASED)
   Mopidy continue to work on Debian/Raspbian stable, where Tornado 2.3 is the
   newest version available.
 
+**Development**
+
+- ``mopidy --version`` and :meth:`mopidy.core.Core.get_version` now returns the
+  correct version when Mopidy is run from a Git repo other than Mopidy's own.
+  (Related to :issue:`706`)
+
 
 v0.19.0 (2014-07-21)
 ====================

mopidy/utils/versioning.py

@@ -1,19 +1,24 @@
 from __future__ import unicode_literals
 
-from subprocess import PIPE, Popen
+import os
+import subprocess
 
-from mopidy import __version__
+import mopidy
 
 
 def get_version():
     try:
         return get_git_version()
     except EnvironmentError:
-        return __version__
+        return mopidy.__version__
 
 
 def get_git_version():
-    process = Popen(['git', 'describe'], stdout=PIPE, stderr=PIPE)
+    project_dir = os.path.abspath(
+        os.path.join(os.path.dirname(mopidy.__file__), '..'))
+    process = subprocess.Popen(
+        ['git', 'describe'],
+        stdout=subprocess.PIPE, stderr=subprocess.PIPE, cwd=project_dir)
     if process.wait() != 0:
         raise EnvironmentError('Execution of "git describe" failed')
     version = process.stdout.read().strip()