Everpad provider crashes on multi-user computer

[hdave]

Steps to reproduce on Ubuntu 12.04 with Everpad 1.5.1

1. Boot up machine
2. User 'A' logs in.
3. Switch user
4. User 'B' logs in.
5. Observe evernote provider crash with the following crash report.

PythonArgs: ['/usr/bin/everpad-provider']
Traceback:
 Traceback (most recent call last):
   File "/usr/bin/everpad-provider", line 9, in <module>
     load_entry_point('everpad==1.5.1dev', 'console_scripts', 'everpad-provider')()
   File "/usr/lib/pymodules/python2.7/everpad/provider/daemon.py", line 60, in main
     fp = open('/tmp/everpad-provider.lock', 'w')
 IOError: [Errno 13] Permission denied: '/tmp/everpad-provider.lock'

The temporary lockfile should probably contain the uid of the user. On this particular computer, its not uncommon to have 5 people logged in via the main console desktop at the same time via 'switch user'.