Reintroduce __version_info__ variable

At least one application (mysql-workbench) (used to) use(s) the __version_info__
that got removed by commit 99859b8b021a5d13ca067a3e79560d6121f9c52f.

Breaking existing software with new versions of paramiko should be avoided.
This pull-request reintroduces the __version_info__ var, but fills it
from the __version__ var. No need to maintain multiple version strings.

Conflicts:
	paramiko/__init__.py
Merge branch '1.8' into 1.9

Conflicts:
	paramiko/__init__.py
Merge branch '1.9' into 1.10

Conflicts:
	paramiko/__init__.py
Merge branch '1.10' into 1.11

Conflicts:
	paramiko/__init__.py
Merge branch '1.11' into 1.12

Conflicts:
	paramiko/__init__.py
New year
No more Python 2.5 on Travis :(
Merge branch '1.8' into 1.9
Merge branch '1.9' into 1.10
Merge branch '1.10' into 1.11
Merge branch '1.11' into 1.12
Merge branch '1.12'
Update travis settings to be similar to fab's
Merge branch '1.8' into 1.9
Merge branch '1.9' into 1.10
Merge branch '1.10' into 1.11
Merge branch '1.11' into 1.12
Merge branch '1.12'
Add a testcase for client.save_host_keys.
No need for 'self.tc' within a single test :)