Remove cPickle session code (fixes #378)
Split up command-line diagnostics into categories

The diagnostics command can now be run separately on the command line. For
example, to only run the email diagnostics, the following command can be
used:

  submin2-admin <submin env> diagnostics email
Add submin2-admin to force recreate svn authz (fixes #380)
Change default vcs_plugins to include git
Fix initenv crash

Do not crash when git_user has not been set yet. This happens for example
when initenv is run (because 'submin2-admin ... git init' has not been run
yet).
Improve submin2-admin initenv questions (refs #355)

The 'initenv' command first asks which features to enable. The questions after
that will depend on which features are enabled. So if one chooses to disable
trac, the trac dir will not be asked. In that case, also the trac deploy will
not be done.

This is also the first time that nginx is enabled by default (only the
creation of config files, like with apache). The default is to enable both
apache as well as nginx.
Fix bug where diagnostics would fail if git was not set yet
Fixed typo
Ask sender email address (fixes #355)

Submin will now set the smtp_from and commit_email_from to a sane default
and will confirm this with the user during initenv.
Update INSTALL docs

 * Add instructions on how to use the command-line diagnostics.
 * Add link to CONFIGURATION for advanced configuration options (refs #355)
Notify user to wait for trac files (fixes #356)

Since the trac files are only created when the user requests trac, we are
not going to spend time to try to make this process quicker.

Instead, notify the user that it might take some time.
Update unittests

In [380e54c551d4b7118353c8d270c4b64b7fb728bd] the default plugins were
changed. This was not changed yet in the unittests.
Diagnostics: test if we can send e-mail (closes #397)

This testing is not waterproof, since the only way to really test is to send
an e-mail and we do not do that. It might help with some basic problems like
bad username/password pair or smtp_hostname is set to a server that doesn't
listen on standard SMTP ports.