Fix for issue #89(Improve savestate error handling)

[XuefengHuang]

I fix savestate error message issue and create a unit test for this PR, this is test result:

Xuefengs-MacBook-Pro:runnable Xuefeng$ python utf.py -f ut_seash_savestate_nicermessage.py 
Testing module: seash
Now starting subprocess: ut_seash_subprocess.py
Generating user keys...
Generating owner key...
Writing config file...
Writing vessel dictionary...
Now running setup script: ut_seash_setup.py
    Running: ut_seash_setup.py                                  [ PASS ]
    Running: ut_seash_savestate_nicermessage.py                 [ PASS ]
Now stopping subprocess: ut_seash_subprocess.py
Removing: v1
Removing: v10
Removing: v2
Removing: v3
Removing: v4
Removing: v5
Removing: v6
Removing: v7
Removing: v8
Removing: v9

[aaaaalbert]

This won't work cross-platform (think Windows).

[asm582]

I have tested this pull request and this can be merged.

Testing by running unit test:

cib@cib-VirtualBox:/seash/RUNNABLE$ python utf.py -f ut_seash_savestate_nicermessageone.py
Testing module: seash
Running: ut_seash_savestate_nicermessageone.py [ PASS ]
cib@cib-VirtualBox:/seash/RUNNABLE$ python utf.py -f ut_seash_savestate_nicermessagetwo.py
Testing module: seash
Running: ut_seash_savestate_nicermessagetwo.py [ PASS ]

Testing by manually entering command on seash:
cib@cib-VirtualBox:~/seash/RUNNABLE$ python seash.py

• You can press the Tab key to enable tab complete when typing commands.

Enabled modules: factoids, geoip, modules, uploaddir, variables

!> savestate NO_KEYS_LOADED
Specify the key name by first typing 'as [username]'.
!> loadkeys guest0
as guest0
!> as guest0
guest0@ !> savestate write_protected_file
Permission denied: write_protected_file
guest0@ !> exit